diff --git a/.idea/runConfigurations/JabRef_Main.xml b/.idea/runConfigurations/JabRef_Main.xml
index 4a1ef684c65..d57c0fd5ac5 100644
--- a/.idea/runConfigurations/JabRef_Main.xml
+++ b/.idea/runConfigurations/JabRef_Main.xml
@@ -2,6 +2,7 @@
   <configuration default="false" name="JabRef Main" type="Application" factoryName="Application" singleton="false">
     <option name="MAIN_CLASS_NAME" value="org.jabref.JabRefMain" />
     <module name="JabRef.main" />
+    <option name="REDIRECT_INPUT" value="true" />
     <option name="VM_PARAMETERS" value="--patch-module test=fastparse_2.12-1.0.0.jar --patch-module test2=fastparse-utils_2.12-1.0.0.jar --patch-module test3=sourcecode_2.12-0.1.4.jar --patch-module org.jabref=build/resources/main --add-exports javafx.controls/com.sun.javafx.scene.control=org.jabref --add-exports org.controlsfx.controls/impl.org.controlsfx.skin=org.jabref --add-opens javafx.controls/javafx.scene.control=org.jabref --add-opens org.controlsfx.controls/org.controlsfx.control.textfield=org.jabref --add-exports javafx.graphics/com.sun.javafx.scene=org.controlsfx.controls --add-exports javafx.graphics/com.sun.javafx.scene.traversal=org.controlsfx.controls --add-exports javafx.graphics/com.sun.javafx.css=org.controlsfx.controls --add-exports javafx.controls/com.sun.javafx.scene.control.behavior=org.controlsfx.controls --add-exports javafx.controls/com.sun.javafx.scene.control=org.controlsfx.controls --add-exports javafx.controls/com.sun.javafx.scene.control.inputmap=org.controlsfx.controls --add-exports javafx.base/com.sun.javafx.event=org.controlsfx.controls --add-exports javafx.base/com.sun.javafx.collections=org.controlsfx.controls --add-exports javafx.base/com.sun.javafx.runtime=org.controlsfx.controls --add-exports javafx.web/com.sun.webkit=org.controlsfx.controls --add-exports javafx.graphics/com.sun.javafx.css=org.controlsfx.controls --add-opens javafx.controls/javafx.scene.control.skin=org.controlsfx.controls --add-opens javafx.graphics/javafx.scene=org.controlsfx.controls --add-exports com.oracle.truffle.regex/com.oracle.truffle.regex=org.graalvm.truffle" />
     <option name="WORKING_DIRECTORY" value="$MODULE_WORKING_DIR$" />
     <RunnerSettings RunnerId="Profile ">
diff --git a/src/main/java/org/jabref/gui/BasePanel.java b/src/main/java/org/jabref/gui/BasePanel.java
index 69ae14cfdff..fcf37459bd6 100644
--- a/src/main/java/org/jabref/gui/BasePanel.java
+++ b/src/main/java/org/jabref/gui/BasePanel.java
@@ -38,7 +38,6 @@
 import org.jabref.model.FieldChange;
 import org.jabref.model.database.BibDatabase;
 import org.jabref.model.database.BibDatabaseContext;
-import org.jabref.model.database.KeyCollisionException;
 import org.jabref.model.database.event.BibDatabaseContextChangedEvent;
 import org.jabref.model.database.event.EntriesAddedEvent;
 import org.jabref.model.database.event.EntriesRemovedEvent;
@@ -253,7 +252,6 @@ public void insertEntry(final BibEntry bibEntry) {
 
     public void insertEntries(final List<BibEntry> entries) {
         if (!entries.isEmpty()) {
-            try {
                 bibDatabaseContext.getDatabase().insertEntries(entries);
 
                 // Set owner and timestamp
@@ -272,9 +270,6 @@ public void insertEntries(final List<BibEntry> entries) {
                     showAndEdit(entries.get(0));
                 }
                 clearAndSelect(entries.get(0));
-            } catch (KeyCollisionException ex) {
-                LOGGER.info("Collision for bibtex key" + ex.getId(), ex);
-            }
         }
     }
 
diff --git a/src/main/java/org/jabref/gui/entryeditor/SourceTab.java b/src/main/java/org/jabref/gui/entryeditor/SourceTab.java
index 47d93fad9cb..c461dc11c1b 100644
--- a/src/main/java/org/jabref/gui/entryeditor/SourceTab.java
+++ b/src/main/java/org/jabref/gui/entryeditor/SourceTab.java
@@ -69,8 +69,8 @@ public class SourceTab extends EntryEditorTab {
     private final DialogService dialogService;
     private final StateManager stateManager;
     private Optional<Pattern> searchHighlightPattern = Optional.empty();
-    private final CodeArea codeArea;
-    private KeyBindingRepository keyBindingRepository;
+    private final KeyBindingRepository keyBindingRepository;
+    private CodeArea codeArea;
 
     private BibEntry previousEntry;
 
@@ -78,7 +78,9 @@ private class EditAction extends SimpleCommand {
 
         private final StandardActions command;
 
-        public EditAction(StandardActions command) { this.command = command; }
+        public EditAction(StandardActions command) {
+            this.command = command;
+        }
 
         @Override
         public void execute() {
@@ -112,11 +114,6 @@ public SourceTab(BibDatabaseContext bibDatabaseContext, CountingUndoManager undo
         this.dialogService = dialogService;
         this.stateManager = stateManager;
         this.keyBindingRepository = keyBindingRepository;
-        this.codeArea = new CodeArea();
-
-        setupSourceEditor();
-        VirtualizedScrollPane<CodeArea> scrollableCodeArea = new VirtualizedScrollPane<>(codeArea);
-        this.setContent(scrollableCodeArea);
 
         stateManager.activeSearchQueryProperty().addListener((observable, oldValue, newValue) -> {
             searchHighlightPattern = newValue.flatMap(SearchQuery::getPatternForWords);
@@ -172,6 +169,7 @@ public Point2D getTextLocation(int offset) {
     }
 
     private void setupSourceEditor() {
+        codeArea = new CodeArea();
         codeArea.setWrapText(true);
         codeArea.setInputMethodRequests(new InputMethodRequestsObject());
         codeArea.setOnInputMethodTextChanged(event -> {
@@ -200,7 +198,7 @@ private void setupSourceEditor() {
             ValidationStatus sourceValidationStatus = sourceValidator.getValidationStatus();
             if (!sourceValidationStatus.isValid()) {
                 sourceValidationStatus.getHighestMessage().ifPresent(message ->
-                    dialogService.showErrorDialogAndWait(message.getMessage()));
+                        dialogService.showErrorDialogAndWait(message.getMessage()));
             }
         });
 
@@ -209,6 +207,8 @@ private void setupSourceEditor() {
                 storeSource(currentEntry, codeArea.textProperty().getValue());
             }
         });
+        VirtualizedScrollPane<CodeArea> scrollableCodeArea = new VirtualizedScrollPane<>(codeArea);
+        this.setContent(scrollableCodeArea);
     }
 
     @Override
@@ -218,6 +218,10 @@ public boolean shouldShow(BibEntry entry) {
 
     private void updateCodeArea() {
         DefaultTaskExecutor.runAndWaitInJavaFXThread(() -> {
+            if (codeArea == null) {
+                setupSourceEditor();
+            }
+
             codeArea.clear();
             try {
                 codeArea.appendText(getSourceString(currentEntry, mode, fieldWriterPreferences));
@@ -233,7 +237,7 @@ private void updateCodeArea() {
 
     @Override
     protected void bindToEntry(BibEntry entry) {
-        if (previousEntry != null) {
+        if (previousEntry != null && codeArea != null) {
             storeSource(previousEntry, codeArea.textProperty().getValue());
         }
         this.previousEntry = entry;
diff --git a/src/main/java/org/jabref/gui/fieldeditors/FieldEditors.java b/src/main/java/org/jabref/gui/fieldeditors/FieldEditors.java
index b8396cedd42..de6b6bd3259 100644
--- a/src/main/java/org/jabref/gui/fieldeditors/FieldEditors.java
+++ b/src/main/java/org/jabref/gui/fieldeditors/FieldEditors.java
@@ -64,7 +64,7 @@ public static FieldEditorFX getForField(final Field field,
             return new JournalEditor(field, journalAbbreviationRepository, preferences, suggestionProvider, fieldCheckers);
         } else if (fieldProperties.contains(FieldProperty.DOI) || fieldProperties.contains(FieldProperty.EPRINT) || fieldProperties.contains(FieldProperty.ISBN)) {
             return new IdentifierEditor(field, taskExecutor, dialogService, suggestionProvider, fieldCheckers, preferences);
-        } else if (field == InternalField.OWNER) {
+        } else if (field == StandardField.OWNER) {
             return new OwnerEditor(field, preferences, suggestionProvider, fieldCheckers);
         } else if (fieldProperties.contains(FieldProperty.FILE_EDITOR)) {
             return new LinkedFilesEditor(field, dialogService, databaseContext, taskExecutor, suggestionProvider, fieldCheckers, preferences);
diff --git a/src/main/java/org/jabref/gui/fieldeditors/FieldNameLabel.java b/src/main/java/org/jabref/gui/fieldeditors/FieldNameLabel.java
index ea4526faa1f..ae3852c3aae 100644
--- a/src/main/java/org/jabref/gui/fieldeditors/FieldNameLabel.java
+++ b/src/main/java/org/jabref/gui/fieldeditors/FieldNameLabel.java
@@ -216,18 +216,18 @@ public String getDescription(Field field) {
                     return Localization.lang("Citation keys of other entries which have a relationship to this entry.");
                 case XREF:
                     return Localization.lang("This field is an alternative cross-referencing mechanism. It differs from \"Crossref\" in that the child entry will not inherit any data from the parent entry specified in the \"Xref\" field.");
-            }
-        } else if (field instanceof InternalField) {
-            InternalField internalField = (InternalField) field;
-            switch (internalField) {
+                case GROUPS:
+                    return Localization.lang("Name(s) of the (manual) groups the entry belongs to.");
                 case OWNER:
                     return Localization.lang("Owner/creator of this entry.");
                 case TIMESTAMP:
                     return Localization.lang("Timestamp of this entry, when it has been created or last modified.");
+            }
+        } else if (field instanceof InternalField) {
+            InternalField internalField = (InternalField) field;
+            switch (internalField) {
                 case KEY_FIELD:
                     return Localization.lang("Key by which the work may be cited.");
-                case GROUPS:
-                    return Localization.lang("Name(s) of the (manual) groups the entry belongs to.");
             }
         } else if (field instanceof SpecialField) {
             SpecialField specialField = (SpecialField) field;
diff --git a/src/main/java/org/jabref/gui/maintable/BibEntryTableViewModel.java b/src/main/java/org/jabref/gui/maintable/BibEntryTableViewModel.java
index 8ef28292285..3db6023abe8 100644
--- a/src/main/java/org/jabref/gui/maintable/BibEntryTableViewModel.java
+++ b/src/main/java/org/jabref/gui/maintable/BibEntryTableViewModel.java
@@ -12,7 +12,6 @@
 import javafx.beans.property.SimpleObjectProperty;
 import javafx.beans.value.ObservableValue;
 
-import org.jabref.Globals;
 import org.jabref.gui.specialfields.SpecialFieldValueViewModel;
 import org.jabref.model.database.BibDatabase;
 import org.jabref.model.database.BibDatabaseContext;
@@ -21,7 +20,6 @@
 import org.jabref.model.entry.LinkedFile;
 import org.jabref.model.entry.field.Field;
 import org.jabref.model.entry.field.FieldProperty;
-import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.OrFields;
 import org.jabref.model.entry.field.SpecialField;
 import org.jabref.model.entry.field.StandardField;
@@ -41,10 +39,10 @@ public class BibEntryTableViewModel {
     private final ObjectBinding<Map<Field, String>> linkedIdentifiers;
     private final ObservableValue<List<AbstractGroup>> matchedGroups;
 
-    public BibEntryTableViewModel(BibEntry entry, BibDatabaseContext database) {
+    public BibEntryTableViewModel(BibEntry entry, BibDatabaseContext database, MainTableNameFormatter nameFormatter) {
         this.entry = entry;
         this.database = database.getDatabase();
-        this.nameFormatter = new MainTableNameFormatter(Globals.prefs);
+        this.nameFormatter = nameFormatter;
 
         this.linkedFiles = EasyBind.map(getField(StandardField.FILE), FileFieldParser::parse);
         this.linkedIdentifiers = createLinkedIdentifiersBinding(entry);
@@ -100,7 +98,7 @@ public ObservableValue<List<AbstractGroup>> getMatchedGroups() {
     private ObservableValue<List<AbstractGroup>> createMatchedGroupsBinding(BibDatabaseContext database) {
         Optional<GroupTreeNode> root = database.getMetaData().getGroups();
         if (root.isPresent()) {
-            return EasyBind.map(entry.getFieldBinding(InternalField.GROUPS), field -> {
+            return EasyBind.map(entry.getFieldBinding(StandardField.GROUPS), field -> {
                 List<AbstractGroup> groups = root.get().getMatchingGroups(entry)
                                                  .stream()
                                                  .map(GroupTreeNode::getGroup)
@@ -122,7 +120,7 @@ public ObservableValue<String> getFields(OrFields fields) {
 
                 Optional<String> content = Optional.empty();
                 for (Field field : fields) {
-                    content = entry.getResolvedFieldOrAlias(field, database);
+                    content = entry.getResolvedFieldOrAliasLatexFree(field, database);
                     if (content.isPresent()) {
                         isName = field.getProperties().contains(FieldProperty.PERSON_NAMES);
                         break;
diff --git a/src/main/java/org/jabref/gui/maintable/MainTableDataModel.java b/src/main/java/org/jabref/gui/maintable/MainTableDataModel.java
index c0ee007455b..c9605508f03 100644
--- a/src/main/java/org/jabref/gui/maintable/MainTableDataModel.java
+++ b/src/main/java/org/jabref/gui/maintable/MainTableDataModel.java
@@ -27,7 +27,8 @@ public class MainTableDataModel {
     public MainTableDataModel(BibDatabaseContext context) {
         ObservableList<BibEntry> allEntries = BindingsHelper.forUI(context.getDatabase().getEntries());
 
-        ObservableList<BibEntryTableViewModel> entriesViewModel = BindingsHelper.mapBacked(allEntries, entry -> new BibEntryTableViewModel(entry, context));
+        MainTableNameFormatter nameFormatter = new MainTableNameFormatter(Globals.prefs);
+        ObservableList<BibEntryTableViewModel> entriesViewModel = BindingsHelper.mapBacked(allEntries, entry -> new BibEntryTableViewModel(entry, context, nameFormatter));
 
         entriesFiltered = new FilteredList<>(entriesViewModel);
         entriesFiltered.predicateProperty().bind(
diff --git a/src/main/java/org/jabref/gui/preferences/TableColumnsTabViewModel.java b/src/main/java/org/jabref/gui/preferences/TableColumnsTabViewModel.java
index 1990315fe01..44c18f3c6a1 100644
--- a/src/main/java/org/jabref/gui/preferences/TableColumnsTabViewModel.java
+++ b/src/main/java/org/jabref/gui/preferences/TableColumnsTabViewModel.java
@@ -61,9 +61,9 @@ public MainTableColumnModel fromString(String string) {
     private final BooleanProperty specialFieldsSerializeProperty = new SimpleBooleanProperty();
     private final BooleanProperty extraFileColumnsEnabledProperty = new SimpleBooleanProperty();
 
-    private Validator columnsNotEmptyValidator;
+    private final Validator columnsNotEmptyValidator;
 
-    private List<String> restartWarnings = new ArrayList<>();
+    private final List<String> restartWarnings = new ArrayList<>();
 
     private final DialogService dialogService;
     private final JabRefPreferences preferences;
@@ -119,9 +119,9 @@ public void setValues() {
                 new MainTableColumnModel(MainTableColumnModel.Type.LINKED_IDENTIFIER),
                 new MainTableColumnModel(MainTableColumnModel.Type.GROUPS),
                 new MainTableColumnModel(MainTableColumnModel.Type.FILES),
-                new MainTableColumnModel(MainTableColumnModel.Type.NORMALFIELD, InternalField.TIMESTAMP.getName()),
-                new MainTableColumnModel(MainTableColumnModel.Type.NORMALFIELD, InternalField.OWNER.getName()),
-                new MainTableColumnModel(MainTableColumnModel.Type.NORMALFIELD, InternalField.GROUPS.getName()),
+                new MainTableColumnModel(MainTableColumnModel.Type.NORMALFIELD, StandardField.TIMESTAMP.getName()),
+                new MainTableColumnModel(MainTableColumnModel.Type.NORMALFIELD, StandardField.OWNER.getName()),
+                new MainTableColumnModel(MainTableColumnModel.Type.NORMALFIELD, StandardField.GROUPS.getName()),
                 new MainTableColumnModel(MainTableColumnModel.Type.NORMALFIELD, InternalField.KEY_FIELD.getName()),
                 new MainTableColumnModel(MainTableColumnModel.Type.NORMALFIELD, InternalField.TYPE_HEADER.getName())
         );
diff --git a/src/main/java/org/jabref/logic/importer/ParserResult.java b/src/main/java/org/jabref/logic/importer/ParserResult.java
index b1f57d207eb..6011dd8e789 100644
--- a/src/main/java/org/jabref/logic/importer/ParserResult.java
+++ b/src/main/java/org/jabref/logic/importer/ParserResult.java
@@ -22,7 +22,6 @@
 public class ParserResult {
     private final Set<BibEntryType> entryTypes;
     private final List<String> warnings = new ArrayList<>();
-    private final List<String> duplicateKeys = new ArrayList<>();
     private BibDatabase database;
     private MetaData metaData;
     private Path file;
@@ -35,7 +34,7 @@ public ParserResult() {
     }
 
     public ParserResult(Collection<BibEntry> entries) {
-        this(BibDatabases.createDatabase(BibDatabases.purgeEmptyEntries(entries)));
+        this(new BibDatabase(BibDatabases.purgeEmptyEntries(entries)));
     }
 
     public ParserResult(BibDatabase database) {
@@ -126,35 +125,6 @@ public List<String> warnings() {
         return new ArrayList<>(warnings);
     }
 
-    /**
-     * Add a key to the list of duplicated BibTeX keys found in the database.
-     *
-     * @param key The duplicated key
-     */
-    public void addDuplicateKey(String key) {
-        if (!duplicateKeys.contains(key)) {
-            duplicateKeys.add(key);
-        }
-    }
-
-    /**
-     * Query whether any duplicated BibTeX keys have been found in the database.
-     *
-     * @return true if there is at least one duplicate key.
-     */
-    public boolean hasDuplicateKeys() {
-        return !duplicateKeys.isEmpty();
-    }
-
-    /**
-     * Get all duplicated keys found in the database.
-     *
-     * @return A list containing the duplicated keys.
-     */
-    public List<String> getDuplicateKeys() {
-        return duplicateKeys;
-    }
-
     public boolean isInvalid() {
         return invalid;
     }
diff --git a/src/main/java/org/jabref/logic/importer/fetcher/DBLPFetcher.java b/src/main/java/org/jabref/logic/importer/fetcher/DBLPFetcher.java
index 2e419a8271d..b8daa91975a 100644
--- a/src/main/java/org/jabref/logic/importer/fetcher/DBLPFetcher.java
+++ b/src/main/java/org/jabref/logic/importer/fetcher/DBLPFetcher.java
@@ -20,7 +20,6 @@
 import org.jabref.model.cleanup.FieldFormatterCleanup;
 import org.jabref.model.cleanup.FieldFormatterCleanups;
 import org.jabref.model.entry.BibEntry;
-import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.util.DummyFileUpdateMonitor;
 
@@ -66,7 +65,7 @@ public void doPostCleanup(BibEntry entry) {
 
         FieldFormatterCleanups cleanups = new FieldFormatterCleanups(true,
                 List.of(
-                        new FieldFormatterCleanup(InternalField.TIMESTAMP, new ClearFormatter()),
+                        new FieldFormatterCleanup(StandardField.TIMESTAMP, new ClearFormatter()),
                         // unescape the the contents of the URL field, e.g., some\_url\_part becomes some_url_part
                         new FieldFormatterCleanup(StandardField.URL, new LayoutFormatterBasedFormatter(new RemoveLatexCommandsFormatter()))
                 ));
diff --git a/src/main/java/org/jabref/logic/importer/fileformat/BibtexParser.java b/src/main/java/org/jabref/logic/importer/fileformat/BibtexParser.java
index d3b1c2ba865..a7d0307efe6 100644
--- a/src/main/java/org/jabref/logic/importer/fileformat/BibtexParser.java
+++ b/src/main/java/org/jabref/logic/importer/fileformat/BibtexParser.java
@@ -38,7 +38,6 @@
 import org.jabref.model.entry.field.Field;
 import org.jabref.model.entry.field.FieldFactory;
 import org.jabref.model.entry.field.FieldProperty;
-import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.entry.types.EntryTypeFactory;
 import org.jabref.model.metadata.MetaData;
@@ -141,11 +140,7 @@ public ParserResult parse(Reader in) throws IOException {
 
         skipWhitespace();
 
-        try {
-            return parseFileContent();
-        } catch (KeyCollisionException kce) {
-            throw new IOException("Duplicate ID in bibtex file: " + kce);
-        }
+        return parseFileContent();
     }
 
     private void initializeParserResult() {
@@ -246,12 +241,7 @@ private void parseAndAddEntry(String type) {
             // store complete parsed serialization (comments, type definition + type contents)
             entry.setParsedSerialization(commentsAndEntryTypeDefinition + dumpTextReadSoFarToString());
 
-            boolean duplicateKey = database.insertEntry(entry);
-            if (duplicateKey) {
-                entry.getField(InternalField.KEY_FIELD).ifPresent(
-                        key -> parserResult.addDuplicateKey(key)
-                );
-            }
+            database.insertEntry(entry);
         } catch (IOException ex) {
             // Trying to make the parser more robust.
             // If an exception is thrown when parsing an entry, drop the entry and try to resume parsing.
@@ -278,7 +268,7 @@ private void parseJabRefComment(Map<String, String> meta) {
         String comment = buffer.toString().replaceAll("[\\x0d\\x0a]", "");
         if (comment.substring(0, Math.min(comment.length(), MetaData.META_FLAG.length())).equals(MetaData.META_FLAG)) {
 
-            if (comment.substring(0, MetaData.META_FLAG.length()).equals(MetaData.META_FLAG)) {
+            if (comment.startsWith(MetaData.META_FLAG)) {
                 String rest = comment.substring(MetaData.META_FLAG.length());
 
                 int pos = rest.indexOf(':');
diff --git a/src/main/java/org/jabref/logic/importer/fileformat/MedlineImporter.java b/src/main/java/org/jabref/logic/importer/fileformat/MedlineImporter.java
index cd91bd6c3c8..c7fc6304bdc 100644
--- a/src/main/java/org/jabref/logic/importer/fileformat/MedlineImporter.java
+++ b/src/main/java/org/jabref/logic/importer/fileformat/MedlineImporter.java
@@ -78,7 +78,6 @@
 import org.jabref.model.entry.Month;
 import org.jabref.model.entry.field.Field;
 import org.jabref.model.entry.field.FieldFactory;
-import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.entry.field.UnknownField;
 import org.jabref.model.entry.types.StandardEntryType;
@@ -372,7 +371,7 @@ private void parseArticle(PubmedArticle article, List<BibEntry> bibItems) {
             }
 
             fields.put(StandardField.PMID, medlineCitation.getPMID().getContent());
-            fields.put(InternalField.OWNER, medlineCitation.getOwner());
+            fields.put(StandardField.OWNER, medlineCitation.getOwner());
 
             addArticleInformation(fields, medlineCitation.getArticle().getContent());
 
diff --git a/src/main/java/org/jabref/logic/importer/fileformat/MedlinePlainImporter.java b/src/main/java/org/jabref/logic/importer/fileformat/MedlinePlainImporter.java
index 1d6d49349e0..5a4b2bcc196 100644
--- a/src/main/java/org/jabref/logic/importer/fileformat/MedlinePlainImporter.java
+++ b/src/main/java/org/jabref/logic/importer/fileformat/MedlinePlainImporter.java
@@ -16,7 +16,6 @@
 import org.jabref.model.entry.AuthorList;
 import org.jabref.model.entry.BibEntry;
 import org.jabref.model.entry.field.Field;
-import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.entry.field.UnknownField;
 import org.jabref.model.entry.types.EntryType;
@@ -170,7 +169,7 @@ public ParserResult importDatabase(BufferedReader reader) throws IOException {
                 hashMap.put("STAT", new UnknownField("status"));
                 hashMap.put("SB", new UnknownField("subset"));
                 hashMap.put("OTO", new UnknownField("termowner"));
-                hashMap.put("OWN", InternalField.OWNER);
+                hashMap.put("OWN", StandardField.OWNER);
 
                 // add the fields to hm
                 for (Map.Entry<String, Field> mapEntry : hashMap.entrySet()) {
diff --git a/src/main/java/org/jabref/logic/util/UpdateField.java b/src/main/java/org/jabref/logic/util/UpdateField.java
index 681571cb53c..5c1a04a6a38 100644
--- a/src/main/java/org/jabref/logic/util/UpdateField.java
+++ b/src/main/java/org/jabref/logic/util/UpdateField.java
@@ -10,7 +10,7 @@
 import org.jabref.model.FieldChange;
 import org.jabref.model.entry.BibEntry;
 import org.jabref.model.entry.field.Field;
-import org.jabref.model.entry.field.InternalField;
+import org.jabref.model.entry.field.StandardField;
 
 public class UpdateField {
 
@@ -95,7 +95,7 @@ public static void setAutomaticFields(BibEntry entry, boolean overwriteOwner, bo
         String defaultOwner = ownerPreferences.getDefaultOwner();
         String timestamp = DateTimeFormatter.ofPattern(timestampPreferences.getTimestampFormat()).format(LocalDateTime.now());
         Field timeStampField = timestampPreferences.getTimestampField();
-        boolean setOwner = ownerPreferences.isUseOwner() && (overwriteOwner || (!entry.hasField(InternalField.OWNER)));
+        boolean setOwner = ownerPreferences.isUseOwner() && (overwriteOwner || (!entry.hasField(StandardField.OWNER)));
         boolean setTimeStamp = timestampPreferences.isUseTimestamps() && (overwriteTimestamp || (!entry.hasField(timeStampField)));
 
         setAutomaticFields(entry, setOwner, defaultOwner, setTimeStamp, timeStampField, timestamp);
@@ -116,7 +116,7 @@ private static void setAutomaticFields(BibEntry entry, boolean setOwner, String
         // Set owner field if this option is enabled:
         if (setOwner) {
             // Set owner field to default value
-            entry.setField(InternalField.OWNER, owner);
+            entry.setField(StandardField.OWNER, owner);
         }
 
         if (setTimeStamp) {
@@ -147,7 +147,7 @@ public static void setAutomaticFields(Collection<BibEntry> bibs, boolean overwri
 
         // Iterate through all entries
         for (BibEntry curEntry : bibs) {
-            boolean setOwner = globalSetOwner && (overwriteOwner || (!curEntry.hasField(InternalField.OWNER)));
+            boolean setOwner = globalSetOwner && (overwriteOwner || (!curEntry.hasField(StandardField.OWNER)));
             boolean setTimeStamp = globalSetTimeStamp && (overwriteTimestamp || (!curEntry.hasField(timeStampField)));
             setAutomaticFields(curEntry, setOwner, defaultOwner, setTimeStamp, timeStampField, timestamp);
         }
diff --git a/src/main/java/org/jabref/model/database/BibDatabase.java b/src/main/java/org/jabref/model/database/BibDatabase.java
index 6496283130a..ea8f1ac2077 100644
--- a/src/main/java/org/jabref/model/database/BibDatabase.java
+++ b/src/main/java/org/jabref/model/database/BibDatabase.java
@@ -169,46 +169,35 @@ public synchronized List<BibEntry> getEntriesByKey(String key) {
     }
 
     /**
-     * Inserts the entry, given that its ID is not already in use.
-     * use Util.createId(...) to make up a unique ID for an entry.
+     * Inserts the entry.
      *
-     * @param entry BibEntry to insert into the database
-     * @return false if the insert was done without a duplicate warning
-     * @throws KeyCollisionException thrown if the entry id ({@link BibEntry#getId()}) is already  present in the database
+     * @param entry entry to insert
      */
-    public synchronized boolean insertEntry(BibEntry entry) throws KeyCollisionException {
-        return insertEntry(entry, EntriesEventSource.LOCAL);
+    public synchronized void insertEntry(BibEntry entry) {
+        insertEntry(entry, EntriesEventSource.LOCAL);
     }
 
     /**
-     * Inserts the entry, given that its ID is not already in use.
-     * use Util.createId(...) to make up a unique ID for an entry.
+     * Inserts the entry.
      *
-     * @param entry BibEntry to insert
-     * @param eventSource Source the event is sent from
-     * @return false if the insert was done without a duplicate warning
+     * @param entry       entry to insert
+     * @param eventSource source the event is sent from
      */
-    public synchronized boolean insertEntry(BibEntry entry, EntriesEventSource eventSource) throws KeyCollisionException {
+    public synchronized void insertEntry(BibEntry entry, EntriesEventSource eventSource) {
         insertEntries(Collections.singletonList(entry), eventSource);
-        return entry.getCiteKeyOptional().map(this::isDuplicateCiteKeyExisting).orElse(false);
     }
 
-    public synchronized void insertEntries(BibEntry... entries) throws KeyCollisionException {
+    public synchronized void insertEntries(BibEntry... entries) {
         insertEntries(Arrays.asList(entries), EntriesEventSource.LOCAL);
     }
 
-    public synchronized void insertEntries(List<BibEntry> entries) throws KeyCollisionException {
+    public synchronized void insertEntries(List<BibEntry> entries) {
         insertEntries(entries, EntriesEventSource.LOCAL);
     }
 
-    public synchronized void insertEntries(List<BibEntry> newEntries, EntriesEventSource eventSource) throws KeyCollisionException {
+    public synchronized void insertEntries(List<BibEntry> newEntries, EntriesEventSource eventSource) {
         Objects.requireNonNull(newEntries);
         for (BibEntry entry : newEntries) {
-            String id = entry.getId();
-            if (containsEntryWithId(id)) {
-                throw new KeyCollisionException("ID is already in use, please choose another", id);
-            }
-
             entry.registerListener(this);
         }
         if (newEntries.isEmpty()) {
diff --git a/src/main/java/org/jabref/model/database/BibDatabases.java b/src/main/java/org/jabref/model/database/BibDatabases.java
index 3d85e693d79..750454c84d1 100644
--- a/src/main/java/org/jabref/model/database/BibDatabases.java
+++ b/src/main/java/org/jabref/model/database/BibDatabases.java
@@ -1,36 +1,16 @@
 package org.jabref.model.database;
 
-import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
 import java.util.stream.Collectors;
 
 import org.jabref.model.entry.BibEntry;
-import org.jabref.model.entry.IdGenerator;
 
 public class BibDatabases {
 
     private BibDatabases() {
     }
 
-    /**
-     * Gets a collection of entries and sets an ID for every entry. After that
-     * all entries are inserted into a new BibDatabase.
-     *
-     * @param entries a collection that contains {@link BibEntry}
-     * @return BibDatabase that contains the entries
-     */
-    public static BibDatabase createDatabase(Collection<BibEntry> entries) {
-        BibDatabase database = new BibDatabase();
-
-        for (BibEntry entry : entries) {
-            entry.setId(IdGenerator.next());
-        }
-        database.insertEntries(new ArrayList<>(entries));
-
-        return database;
-    }
-
     /**
      * Receives a Collection of BibEntry instances, iterates through them, and
      * removes all entries that have no fields set. This is useful for rooting out
diff --git a/src/main/java/org/jabref/model/entry/BibEntry.java b/src/main/java/org/jabref/model/entry/BibEntry.java
index 0bfe4f7b11b..7092d6af4d9 100644
--- a/src/main/java/org/jabref/model/entry/BibEntry.java
+++ b/src/main/java/org/jabref/model/entry/BibEntry.java
@@ -70,7 +70,7 @@ public class BibEntry implements Cloneable {
     /**
      * Cache that stores the field as keyword lists (format &lt;Field, Separator, Keyword list>)
      */
-    private final MultiKeyMap<Field, Character, KeywordList> fieldsAsKeywords = new MultiKeyMap<>();
+    private final MultiKeyMap<StandardField, Character, KeywordList> fieldsAsKeywords = new MultiKeyMap<>(StandardField.class);
 
     private final EventBus eventBus = new EventBus();
     private String id;
@@ -91,28 +91,16 @@ public class BibEntry implements Cloneable {
      * Constructs a new BibEntry. The internal ID is set to IdGenerator.next()
      */
     public BibEntry() {
-        this(IdGenerator.next(), DEFAULT_TYPE);
-    }
-
-    /**
-     * Constructs a new BibEntry with the given ID and given type
-     *
-     * @param id   The ID to be used
-     * @param type The type to set. May be null or empty. In that case, DEFAULT_TYPE is used.
-     */
-    private BibEntry(String id, EntryType type) {
-        Objects.requireNonNull(id, "Every BibEntry must have an ID");
-
-        this.id = id;
-        setType(type);
-        this.sharedBibEntryData = new SharedBibEntryData();
+        this(DEFAULT_TYPE);
     }
 
     /**
      * Constructs a new BibEntry. The internal ID is set to IdGenerator.next()
      */
     public BibEntry(EntryType type) {
-        this(IdGenerator.next(), type);
+        this.id = IdGenerator.next();
+        setType(type);
+        this.sharedBibEntryData = new SharedBibEntryData();
     }
 
     public Optional<FieldChange> setMonth(Month parsedMonth) {
@@ -621,7 +609,7 @@ public boolean allFieldsPresent(Collection<OrFields> fields, BibDatabase databas
      */
     @Override
     public Object clone() {
-        BibEntry clone = new BibEntry(IdGenerator.next(), type.getValue());
+        BibEntry clone = new BibEntry(type.getValue());
         clone.fields = FXCollections.observableMap(new ConcurrentHashMap<>(fields));
         return clone;
     }
@@ -856,16 +844,21 @@ public Set<String> getFieldAsWords(Field field) {
     }
 
     public KeywordList getFieldAsKeywords(Field field, Character keywordSeparator) {
-        Optional<KeywordList> storedList = fieldsAsKeywords.get(field, keywordSeparator);
-        if (storedList.isPresent()) {
-            return storedList.get();
-        } else {
-            KeywordList keywords = getField(field)
-                    .map(content -> KeywordList.parse(content, keywordSeparator))
-                    .orElse(new KeywordList());
-            fieldsAsKeywords.put(field, keywordSeparator, keywords);
-            return keywords;
+        if (field instanceof StandardField) {
+            Optional<KeywordList> storedList = fieldsAsKeywords.get((StandardField) field, keywordSeparator);
+            if (storedList.isPresent()) {
+                return storedList.get();
+            }
         }
+
+        KeywordList keywords = getField(field)
+                .map(content -> KeywordList.parse(content, keywordSeparator))
+                .orElse(new KeywordList());
+
+        if (field instanceof StandardField) {
+            fieldsAsKeywords.put((StandardField) field, keywordSeparator, keywords);
+        }
+        return keywords;
     }
 
     public Optional<FieldChange> clearCiteKey() {
@@ -875,7 +868,10 @@ public Optional<FieldChange> clearCiteKey() {
     private void invalidateFieldCache(Field field) {
         latexFreeFields.remove(field);
         fieldsAsWords.remove(field);
-        fieldsAsKeywords.remove(field);
+
+        if (field instanceof StandardField) {
+            fieldsAsKeywords.remove((StandardField) field);
+        }
     }
 
     public Optional<String> getLatexFreeField(Field field) {
diff --git a/src/main/java/org/jabref/model/entry/field/FieldFactory.java b/src/main/java/org/jabref/model/entry/field/FieldFactory.java
index a5086283f6a..8c99795ed37 100644
--- a/src/main/java/org/jabref/model/entry/field/FieldFactory.java
+++ b/src/main/java/org/jabref/model/entry/field/FieldFactory.java
@@ -134,7 +134,7 @@ private static Set<Field> getAllFields() {
      * separate preferences object
      */
     public static List<Field> getDefaultGeneralFields() {
-        List<Field> defaultGeneralFields = new ArrayList<>(Arrays.asList(StandardField.DOI, StandardField.CROSSREF, StandardField.KEYWORDS, StandardField.EPRINT, StandardField.URL, StandardField.FILE, InternalField.GROUPS, InternalField.OWNER, InternalField.TIMESTAMP));
+        List<Field> defaultGeneralFields = new ArrayList<>(Arrays.asList(StandardField.DOI, StandardField.CROSSREF, StandardField.KEYWORDS, StandardField.EPRINT, StandardField.URL, StandardField.FILE, StandardField.GROUPS, StandardField.OWNER, StandardField.TIMESTAMP));
         defaultGeneralFields.addAll(EnumSet.allOf(SpecialField.class));
         return defaultGeneralFields;
     }
diff --git a/src/main/java/org/jabref/model/entry/field/InternalField.java b/src/main/java/org/jabref/model/entry/field/InternalField.java
index 9fabf4801e1..3ee97e605c2 100644
--- a/src/main/java/org/jabref/model/entry/field/InternalField.java
+++ b/src/main/java/org/jabref/model/entry/field/InternalField.java
@@ -7,12 +7,9 @@
 import java.util.Set;
 
 /**
- * JabRef internal fields
+ * JabRef internal fields. These are not normal fields but mostly place holders with special functions.
  */
 public enum InternalField implements Field {
-    OWNER("owner"),
-    TIMESTAMP("timestamp", FieldProperty.DATE),
-    GROUPS("groups"),
     KEY_FIELD("bibtexkey"),
     /**
      * field which indicates the entrytype
diff --git a/src/main/java/org/jabref/model/entry/field/SpecialField.java b/src/main/java/org/jabref/model/entry/field/SpecialField.java
index 2f54fd7bad4..188b37e7370 100644
--- a/src/main/java/org/jabref/model/entry/field/SpecialField.java
+++ b/src/main/java/org/jabref/model/entry/field/SpecialField.java
@@ -37,19 +37,19 @@ public enum SpecialField implements Field {
     ),
 
     READ_STATUS("readstatus",
-        SpecialFieldValue.CLEAR_READ_STATUS,
-        SpecialFieldValue.READ,
-        SpecialFieldValue.SKIMMED
+            SpecialFieldValue.CLEAR_READ_STATUS,
+            SpecialFieldValue.READ,
+            SpecialFieldValue.SKIMMED
     ),
 
     RELEVANCE("relevance",
-        SpecialFieldValue.RELEVANT
+            SpecialFieldValue.RELEVANT
     );
 
-    private List<SpecialFieldValue> values;
-    private KeywordList keywords;
-    private HashMap<String, SpecialFieldValue> map;
-    private String fieldName;
+    private final List<SpecialFieldValue> values;
+    private final KeywordList keywords;
+    private final HashMap<String, SpecialFieldValue> map;
+    private final String fieldName;
 
     SpecialField(String fieldName, SpecialFieldValue... values) {
         this.fieldName = fieldName;
diff --git a/src/main/java/org/jabref/model/entry/field/StandardField.java b/src/main/java/org/jabref/model/entry/field/StandardField.java
index 6f10d4e0c57..a79a4208e4b 100644
--- a/src/main/java/org/jabref/model/entry/field/StandardField.java
+++ b/src/main/java/org/jabref/model/entry/field/StandardField.java
@@ -7,7 +7,7 @@
 import java.util.Set;
 
 /**
- * Standard BibTeX and BibLaTeX fields
+ * Standard BibTeX and BibLaTeX fields, as well as "normal" JabRef specific fields.
  */
 public enum StandardField implements Field {
 
@@ -124,7 +124,12 @@ public enum StandardField implements Field {
     YEARFILED("yearfiled"),
     MR_NUMBER("mrnumber"),
     XDATA("xdata", FieldProperty.MULTIPLE_ENTRY_LINK),
-    XREF("xref", FieldProperty.SINGLE_ENTRY_LINK);
+    XREF("xref", FieldProperty.SINGLE_ENTRY_LINK),
+
+    // JabRef-specific fields
+    GROUPS("groups"),
+    OWNER("owner"),
+    TIMESTAMP("timestamp", FieldProperty.DATE);
 
     private final String name;
     private final String displayName;
diff --git a/src/main/java/org/jabref/model/groups/AutomaticKeywordGroup.java b/src/main/java/org/jabref/model/groups/AutomaticKeywordGroup.java
index 12c12f7b05c..06dfcd983c1 100644
--- a/src/main/java/org/jabref/model/groups/AutomaticKeywordGroup.java
+++ b/src/main/java/org/jabref/model/groups/AutomaticKeywordGroup.java
@@ -1,7 +1,6 @@
 package org.jabref.model.groups;
 
 import java.util.Objects;
-import java.util.Optional;
 import java.util.Set;
 import java.util.stream.Collectors;
 
@@ -10,13 +9,12 @@
 import org.jabref.model.entry.KeywordList;
 import org.jabref.model.entry.field.Field;
 import org.jabref.model.strings.StringUtil;
-import org.jabref.model.util.OptionalUtil;
 
 public class AutomaticKeywordGroup extends AutomaticGroup {
 
-    private Character keywordDelimiter;
-    private Character keywordHierarchicalDelimiter;
-    private Field field;
+    private final Character keywordDelimiter;
+    private final Character keywordHierarchicalDelimiter;
+    private final Field field;
 
     public AutomaticKeywordGroup(String name, GroupHierarchyType context, Field field, Character keywordDelimiter, Character keywordHierarchicalDelimiter) {
         super(name, context);
@@ -62,13 +60,11 @@ public int hashCode() {
 
     @Override
     public Set<GroupTreeNode> createSubgroups(BibEntry entry) {
-        Optional<KeywordList> keywordList = entry.getLatexFreeField(field)
-                                                 .map(fieldValue -> KeywordList.parse(fieldValue, keywordDelimiter));
-        return OptionalUtil.toStream(keywordList)
-                           .flatMap(KeywordList::stream)
-                           .filter(keyword -> StringUtil.isNotBlank(keyword.get()))
-                           .map(this::createGroup)
-                           .collect(Collectors.toSet());
+        KeywordList keywordList = entry.getFieldAsKeywords(field, keywordDelimiter);
+        return keywordList.stream()
+                          .filter(keyword -> StringUtil.isNotBlank(keyword.get()))
+                          .map(this::createGroup)
+                          .collect(Collectors.toSet());
     }
 
     private GroupTreeNode createGroup(Keyword keywordChain) {
diff --git a/src/main/java/org/jabref/model/groups/ExplicitGroup.java b/src/main/java/org/jabref/model/groups/ExplicitGroup.java
index d05c8531ceb..53a01bc519d 100644
--- a/src/main/java/org/jabref/model/groups/ExplicitGroup.java
+++ b/src/main/java/org/jabref/model/groups/ExplicitGroup.java
@@ -5,13 +5,13 @@
 import java.util.List;
 import java.util.Objects;
 
-import org.jabref.model.entry.field.InternalField;
+import org.jabref.model.entry.field.StandardField;
 
 /**
  * This group contains entries, which were manually assigned to it.
- * Assignments are stored in the {@link InternalField#GROUPS} field.
+ * Assignments are stored in the {@link StandardField#GROUPS} field.
  * Thus, internally, we represent {@link ExplicitGroup} as a special {@link WordKeywordGroup} operating on
- * {@link InternalField#GROUPS}.
+ * {@link StandardField#GROUPS}.
  */
 public class ExplicitGroup extends WordKeywordGroup {
 
@@ -22,7 +22,7 @@ public class ExplicitGroup extends WordKeywordGroup {
     private final List<String> legacyEntryKeys = new ArrayList<>();
 
     public ExplicitGroup(String name, GroupHierarchyType context, Character keywordSeparator) {
-        super(name, context, InternalField.GROUPS, name, true, keywordSeparator, true);
+        super(name, context, StandardField.GROUPS, name, true, keywordSeparator, true);
     }
 
     public void addLegacyEntryKey(String key) {
diff --git a/src/main/java/org/jabref/model/groups/WordKeywordGroup.java b/src/main/java/org/jabref/model/groups/WordKeywordGroup.java
index c4d4432ee62..46ca9fc7e49 100644
--- a/src/main/java/org/jabref/model/groups/WordKeywordGroup.java
+++ b/src/main/java/org/jabref/model/groups/WordKeywordGroup.java
@@ -13,7 +13,10 @@
 import org.jabref.model.entry.KeywordList;
 import org.jabref.model.entry.field.Field;
 import org.jabref.model.entry.field.InternalField;
+import org.jabref.model.entry.types.EntryType;
+import org.jabref.model.entry.types.EntryTypeFactory;
 import org.jabref.model.strings.StringUtil;
+import org.jabref.model.util.ListUtil;
 
 /**
  * Matches entries if a given field contains a specified word.
@@ -21,7 +24,7 @@
 public class WordKeywordGroup extends KeywordGroup implements GroupEntryChanger {
 
     protected final Character keywordSeparator;
-    private final Set<String> searchWords;
+    private final SearchStrategy searchStrategy;
     private final boolean onlySplitWordsAtSeparator;
 
     public WordKeywordGroup(String name, GroupHierarchyType context, Field searchField,
@@ -31,7 +34,16 @@ public WordKeywordGroup(String name, GroupHierarchyType context, Field searchFie
 
         this.keywordSeparator = keywordSeparator;
         this.onlySplitWordsAtSeparator = onlySplitWordsAtSeparator;
-        this.searchWords = getSearchWords(searchExpression);
+
+        if (onlySplitWordsAtSeparator) {
+            if (InternalField.TYPE_HEADER.equals(searchField)) {
+                searchStrategy = new TypeSearchStrategy();
+            } else {
+                searchStrategy = new KeywordListSearchStrategy();
+            }
+        } else {
+            searchStrategy = new StringSearchStrategy();
+        }
     }
 
     private static boolean containsCaseInsensitive(Set<String> searchIn, Collection<String> searchFor) {
@@ -105,31 +117,7 @@ public boolean equals(Object o) {
 
     @Override
     public boolean contains(BibEntry entry) {
-        Set<String> content = getFieldContentAsWords(entry);
-        if (caseSensitive) {
-            return content.containsAll(searchWords);
-        } else {
-            return containsCaseInsensitive(content, searchWords);
-        }
-    }
-
-    private Set<String> getFieldContentAsWords(BibEntry entry) {
-        if (onlySplitWordsAtSeparator) {
-            if (InternalField.TYPE_HEADER.equals(searchField)) {
-                return searchWords.stream().filter(word -> entry.getType().getName().equalsIgnoreCase(word)).collect(Collectors.toSet());
-            }
-            return entry.getFieldAsKeywords(searchField, keywordSeparator).toStringList();
-        } else {
-            return entry.getFieldAsWords(searchField);
-        }
-    }
-
-    private Set<String> getSearchWords(String searchExpression) {
-        if (onlySplitWordsAtSeparator) {
-            return KeywordList.parse(searchExpression, keywordSeparator).toStringList();
-        } else {
-            return new HashSet<>(StringUtil.getStringAsWords(searchExpression));
-        }
+        return searchStrategy.contains(entry);
     }
 
     @Override
@@ -148,4 +136,59 @@ public int hashCode() {
                 keywordSeparator,
                 onlySplitWordsAtSeparator);
     }
+
+    interface SearchStrategy {
+        boolean contains(BibEntry entry);
+    }
+
+    class StringSearchStrategy implements SearchStrategy {
+        Set<String> searchWords;
+
+        StringSearchStrategy() {
+            searchWords = new HashSet<>(StringUtil.getStringAsWords(searchExpression));
+        }
+
+        @Override
+        public boolean contains(BibEntry entry) {
+            Set<String> content = entry.getFieldAsWords(searchField);
+            if (caseSensitive) {
+                return content.containsAll(searchWords);
+            } else {
+                return containsCaseInsensitive(content, searchWords);
+            }
+        }
+    }
+
+    class TypeSearchStrategy implements SearchStrategy {
+
+        Set<EntryType> searchWords;
+
+        TypeSearchStrategy() {
+            searchWords = KeywordList.parse(searchExpression, keywordSeparator)
+                                     .stream()
+                                     .map(word -> EntryTypeFactory.parse(word.get()))
+                                     .collect(Collectors.toSet());
+        }
+
+        @Override
+        public boolean contains(BibEntry entry) {
+            return searchWords.stream()
+                              .anyMatch(word -> entry.getType().equals(word));
+        }
+    }
+
+    class KeywordListSearchStrategy implements SearchStrategy {
+
+        private final KeywordList searchWords;
+
+        KeywordListSearchStrategy() {
+            searchWords = KeywordList.parse(searchExpression, keywordSeparator);
+        }
+
+        @Override
+        public boolean contains(BibEntry entry) {
+            KeywordList fieldValue = entry.getFieldAsKeywords(searchField, keywordSeparator);
+            return ListUtil.allMatch(searchWords, fieldValue::contains);
+        }
+    }
 }
diff --git a/src/main/java/org/jabref/model/search/matchers/OrMatcher.java b/src/main/java/org/jabref/model/search/matchers/OrMatcher.java
index c0a0eddf1d9..578b2b97c00 100644
--- a/src/main/java/org/jabref/model/search/matchers/OrMatcher.java
+++ b/src/main/java/org/jabref/model/search/matchers/OrMatcher.java
@@ -1,6 +1,7 @@
 package org.jabref.model.search.matchers;
 
 import org.jabref.model.entry.BibEntry;
+import org.jabref.model.util.ListUtil;
 
 /**
  * A set of matchers that returns true if any matcher matches the given entry.
@@ -9,7 +10,6 @@ public class OrMatcher extends MatcherSet {
 
     @Override
     public boolean isMatch(BibEntry entry) {
-        return matchers.stream()
-                       .anyMatch(rule -> rule.isMatch(entry));
+        return ListUtil.anyMatch(matchers, rule -> rule.isMatch(entry));
     }
 }
diff --git a/src/main/java/org/jabref/model/util/ListUtil.java b/src/main/java/org/jabref/model/util/ListUtil.java
new file mode 100644
index 00000000000..9f9589b05ab
--- /dev/null
+++ b/src/main/java/org/jabref/model/util/ListUtil.java
@@ -0,0 +1,33 @@
+package org.jabref.model.util;
+
+import java.util.function.Predicate;
+
+/**
+ * Provides a few helper methods for lists.
+ */
+public class ListUtil {
+
+    /**
+     * Equivalent to list.stream().anyMatch but with slightly better performance (especially for small lists).
+     */
+    public static <T> boolean anyMatch(Iterable<T> list, Predicate<T> predicate) {
+        for (T element : list) {
+            if (predicate.test(element)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Equivalent to list.stream().allMatch but with slightly better performance (especially for small lists).
+     */
+    public static <T> boolean allMatch(Iterable<T> list, Predicate<T> predicate) {
+        for (T element : list) {
+            if (!predicate.test(element)) {
+                return false;
+            }
+        }
+        return true;
+    }
+}
diff --git a/src/main/java/org/jabref/model/util/MultiKeyMap.java b/src/main/java/org/jabref/model/util/MultiKeyMap.java
index c5ba8bbfbf4..f732724a26f 100644
--- a/src/main/java/org/jabref/model/util/MultiKeyMap.java
+++ b/src/main/java/org/jabref/model/util/MultiKeyMap.java
@@ -1,11 +1,16 @@
 package org.jabref.model.util;
 
+import java.util.EnumMap;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
 
-public class MultiKeyMap<K1, K2, V> {
-    private final Map<K1, Map<K2, V>> map = new HashMap<>();
+public class MultiKeyMap<K1 extends Enum<K1>, K2, V> {
+    private final EnumMap<K1, Map<K2, V>> map;
+
+    public MultiKeyMap(Class<K1> keyType) {
+        map = new EnumMap<>(keyType);
+    }
 
     public Optional<V> get(K1 key1, K2 key2) {
         Map<K2, V> metaValue = map.get(key1);
diff --git a/src/main/java/org/jabref/preferences/JabRefPreferences.java b/src/main/java/org/jabref/preferences/JabRefPreferences.java
index 9af9a2a81c1..e920c014f7a 100644
--- a/src/main/java/org/jabref/preferences/JabRefPreferences.java
+++ b/src/main/java/org/jabref/preferences/JabRefPreferences.java
@@ -579,7 +579,7 @@ private JabRefPreferences() {
         // default time stamp follows ISO-8601. Reason: https://xkcd.com/1179/
         defaults.put(TIME_STAMP_FORMAT, "yyyy-MM-dd");
 
-        defaults.put(TIME_STAMP_FIELD, InternalField.TIMESTAMP.getName());
+        defaults.put(TIME_STAMP_FIELD, StandardField.TIMESTAMP.getName());
         defaults.put(UPDATE_TIMESTAMP, Boolean.FALSE);
 
         defaults.put(GENERATE_KEYS_BEFORE_SAVING, Boolean.FALSE);
diff --git a/src/test/java/org/jabref/gui/UpdateTimestampListenerTest.java b/src/test/java/org/jabref/gui/UpdateTimestampListenerTest.java
index 283de46541b..512beaf6c6a 100644
--- a/src/test/java/org/jabref/gui/UpdateTimestampListenerTest.java
+++ b/src/test/java/org/jabref/gui/UpdateTimestampListenerTest.java
@@ -6,7 +6,7 @@
 import org.jabref.model.database.BibDatabase;
 import org.jabref.model.entry.BibEntry;
 import org.jabref.model.entry.field.Field;
-import org.jabref.model.entry.field.InternalField;
+import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.entry.field.UnknownField;
 import org.jabref.preferences.JabRefPreferences;
 
@@ -40,7 +40,7 @@ void setUp() {
 
     @Test
     void updateTimestampEnabled() {
-        final Field timestampField = InternalField.TIMESTAMP;
+        final Field timestampField = StandardField.TIMESTAMP;
         final String baseDate = "2000-1-1";
         final String newDate = "2000-1-2";
 
@@ -63,7 +63,7 @@ void updateTimestampEnabled() {
 
     @Test
     void updateTimestampDisabled() {
-        final Field timestampField = InternalField.TIMESTAMP;
+        final Field timestampField = StandardField.TIMESTAMP;
         final String baseDate = "2000-1-1";
         final String newDate = "2000-1-2";
 
diff --git a/src/test/java/org/jabref/gui/groups/GroupNodeViewModelTest.java b/src/test/java/org/jabref/gui/groups/GroupNodeViewModelTest.java
index 90af41c477c..c3bfb662aaf 100644
--- a/src/test/java/org/jabref/gui/groups/GroupNodeViewModelTest.java
+++ b/src/test/java/org/jabref/gui/groups/GroupNodeViewModelTest.java
@@ -12,7 +12,6 @@
 import org.jabref.gui.util.TaskExecutor;
 import org.jabref.model.database.BibDatabaseContext;
 import org.jabref.model.entry.BibEntry;
-import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.groups.AbstractGroup;
 import org.jabref.model.groups.AutomaticKeywordGroup;
@@ -29,7 +28,7 @@
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
-public class GroupNodeViewModelTest {
+class GroupNodeViewModelTest {
 
     private StateManager stateManager;
     private BibDatabaseContext databaseContext;
@@ -37,7 +36,7 @@ public class GroupNodeViewModelTest {
     private TaskExecutor taskExecutor;
 
     @BeforeEach
-    public void setUp() throws Exception {
+    void setUp() throws Exception {
         stateManager = mock(StateManager.class);
         when(stateManager.getSelectedEntries()).thenReturn(FXCollections.emptyObservableList());
         databaseContext = new BibDatabaseContext();
@@ -48,24 +47,24 @@ public void setUp() throws Exception {
     }
 
     @Test
-    public void getDisplayNameConvertsLatexToUnicode() throws Exception {
+    void getDisplayNameConvertsLatexToUnicode() throws Exception {
         GroupNodeViewModel viewModel = getViewModelForGroup(
                 new WordKeywordGroup("\\beta", GroupHierarchyType.INDEPENDENT, StandardField.TITLE, "search", true, ',', false));
         assertEquals("β", viewModel.getDisplayName());
     }
 
     @Test
-    public void alwaysMatchedByEmptySearchString() throws Exception {
+    void alwaysMatchedByEmptySearchString() throws Exception {
         assertTrue(viewModel.isMatchedBy(""));
     }
 
     @Test
-    public void isMatchedIfContainsPartOfSearchString() throws Exception {
+    void isMatchedIfContainsPartOfSearchString() throws Exception {
         assertTrue(viewModel.isMatchedBy("est"));
     }
 
     @Test
-    public void treeOfAutomaticKeywordGroupIsCombined() throws Exception {
+    void treeOfAutomaticKeywordGroupIsCombined() throws Exception {
         BibEntry entryOne = new BibEntry().withField(StandardField.KEYWORDS, "A > B > B1, A > C");
         BibEntry entryTwo = new BibEntry().withField(StandardField.KEYWORDS, "A > D, E");
         BibEntry entryThree = new BibEntry().withField(StandardField.KEYWORDS, "A > B > B2");
@@ -94,7 +93,7 @@ public void treeOfAutomaticKeywordGroupIsCombined() throws Exception {
     }
 
     @Test
-    public void draggedOnTopOfGroupAddsBeforeIt() throws Exception {
+    void draggedOnTopOfGroupAddsBeforeIt() throws Exception {
         GroupNodeViewModel rootViewModel = getViewModelForGroup(new WordKeywordGroup("root", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A", true, ',', true));
         WordKeywordGroup groupA = new WordKeywordGroup("A", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A", true, ',', true);
         WordKeywordGroup groupB = new WordKeywordGroup("B", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A > B", true, ',', true);
@@ -109,7 +108,7 @@ public void draggedOnTopOfGroupAddsBeforeIt() throws Exception {
     }
 
     @Test
-    public void draggedOnBottomOfGroupAddsAfterIt() throws Exception {
+    void draggedOnBottomOfGroupAddsAfterIt() throws Exception {
         GroupNodeViewModel rootViewModel = getViewModelForGroup(new WordKeywordGroup("root", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A", true, ',', true));
         WordKeywordGroup groupA = new WordKeywordGroup("A", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A", true, ',', true);
         WordKeywordGroup groupB = new WordKeywordGroup("B", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A > B", true, ',', true);
@@ -124,7 +123,7 @@ public void draggedOnBottomOfGroupAddsAfterIt() throws Exception {
     }
 
     @Test
-    public void draggedOnBottomOfGroupAddsAfterItWhenSourceGroupWasBefore() throws Exception {
+    void draggedOnBottomOfGroupAddsAfterItWhenSourceGroupWasBefore() throws Exception {
         GroupNodeViewModel rootViewModel = getViewModelForGroup(new WordKeywordGroup("root", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A", true, ',', true));
         WordKeywordGroup groupA = new WordKeywordGroup("A", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A", true, ',', true);
         WordKeywordGroup groupB = new WordKeywordGroup("B", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A > B", true, ',', true);
@@ -139,7 +138,7 @@ public void draggedOnBottomOfGroupAddsAfterItWhenSourceGroupWasBefore() throws E
     }
 
     @Test
-    public void draggedOnTopOfGroupAddsBeforeItWhenSourceGroupWasBefore() throws Exception {
+    void draggedOnTopOfGroupAddsBeforeItWhenSourceGroupWasBefore() throws Exception {
         GroupNodeViewModel rootViewModel = getViewModelForGroup(new WordKeywordGroup("root", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A", true, ',', true));
         WordKeywordGroup groupA = new WordKeywordGroup("A", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A", true, ',', true);
         WordKeywordGroup groupB = new WordKeywordGroup("B", GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, "A > B", true, ',', true);
@@ -154,7 +153,7 @@ public void draggedOnTopOfGroupAddsBeforeItWhenSourceGroupWasBefore() throws Exc
     }
 
     @Test
-    public void entriesAreAddedCorrectly() {
+    void entriesAreAddedCorrectly() {
         String groupName = "group";
         ExplicitGroup group = new ExplicitGroup(groupName, GroupHierarchyType.INDEPENDENT, ',');
         BibEntry entry = new BibEntry();
@@ -164,7 +163,7 @@ public void entriesAreAddedCorrectly() {
         model.addEntriesToGroup(databaseContext.getEntries());
 
         assertEquals(databaseContext.getEntries(), model.getGroupNode().getEntriesInGroup(databaseContext.getEntries()));
-        assertEquals(groupName, entry.getField(InternalField.GROUPS).get());
+        assertEquals(groupName, entry.getField(StandardField.GROUPS).get());
     }
 
     private GroupNodeViewModel getViewModelForGroup(AbstractGroup group) {
diff --git a/src/test/java/org/jabref/gui/groups/GroupTreeViewModelTest.java b/src/test/java/org/jabref/gui/groups/GroupTreeViewModelTest.java
index 40d37af02b4..7eb1c213f4f 100644
--- a/src/test/java/org/jabref/gui/groups/GroupTreeViewModelTest.java
+++ b/src/test/java/org/jabref/gui/groups/GroupTreeViewModelTest.java
@@ -9,7 +9,6 @@
 import org.jabref.gui.util.TaskExecutor;
 import org.jabref.model.database.BibDatabaseContext;
 import org.jabref.model.entry.BibEntry;
-import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.groups.AllEntriesGroup;
 import org.jabref.model.groups.ExplicitGroup;
@@ -23,14 +22,14 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.mockito.Mockito.mock;
 
-public class GroupTreeViewModelTest {
+class GroupTreeViewModelTest {
     StateManager stateManager;
     GroupTreeViewModel groupTree;
     BibDatabaseContext databaseContext;
     private TaskExecutor taskExecutor;
 
     @BeforeEach
-    public void setUp() throws Exception {
+    void setUp() throws Exception {
         databaseContext = new BibDatabaseContext();
         stateManager = new StateManager();
         stateManager.activeDatabaseProperty().setValue(Optional.of(databaseContext));
@@ -39,13 +38,13 @@ public void setUp() throws Exception {
     }
 
     @Test
-    public void rootGroupIsAllEntriesByDefault() throws Exception {
+    void rootGroupIsAllEntriesByDefault() throws Exception {
         AllEntriesGroup allEntriesGroup = new AllEntriesGroup("All entries");
         assertEquals(new GroupNodeViewModel(databaseContext, stateManager, taskExecutor, allEntriesGroup, new CustomLocalDragboard()), groupTree.rootGroupProperty().getValue());
     }
 
     @Test
-    public void explicitGroupsAreRemovedFromEntriesOnDelete() {
+    void explicitGroupsAreRemovedFromEntriesOnDelete() {
         ExplicitGroup group = new ExplicitGroup("group", GroupHierarchyType.INDEPENDENT, ',');
         BibEntry entry = new BibEntry();
         databaseContext.getDatabase().insertEntry(entry);
@@ -54,11 +53,11 @@ public void explicitGroupsAreRemovedFromEntriesOnDelete() {
         model.addEntriesToGroup(databaseContext.getEntries());
         groupTree.removeGroupsAndSubGroupsFromEntries(model);
 
-        assertEquals(Optional.empty(), entry.getField(InternalField.GROUPS));
+        assertEquals(Optional.empty(), entry.getField(StandardField.GROUPS));
     }
 
     @Test
-    public void keywordGroupsAreNotRemovedFromEntriesOnDelete() {
+    void keywordGroupsAreNotRemovedFromEntriesOnDelete() {
         String groupName = "A";
         WordKeywordGroup group = new WordKeywordGroup(groupName, GroupHierarchyType.INCLUDING, StandardField.KEYWORDS, groupName, true, ',', true);
         BibEntry entry = new BibEntry();
diff --git a/src/test/java/org/jabref/logic/importer/fetcher/MedlineFetcherTest.java b/src/test/java/org/jabref/logic/importer/fetcher/MedlineFetcherTest.java
index ada1b137b35..7eda3871267 100644
--- a/src/test/java/org/jabref/logic/importer/fetcher/MedlineFetcherTest.java
+++ b/src/test/java/org/jabref/logic/importer/fetcher/MedlineFetcherTest.java
@@ -5,7 +5,6 @@
 import java.util.Optional;
 
 import org.jabref.model.entry.BibEntry;
-import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.entry.field.UnknownField;
 import org.jabref.model.entry.types.StandardEntryType;
@@ -41,7 +40,7 @@ public void setUp() throws InterruptedException {
         entryWijedasa.setField(StandardField.JOURNAL, "Global change biology");
         entryWijedasa.setField(StandardField.MONTH, "#mar#");
         entryWijedasa.setField(new UnknownField("nlm-id"), "9888746");
-        entryWijedasa.setField(InternalField.OWNER, "NLM");
+        entryWijedasa.setField(StandardField.OWNER, "NLM");
         entryWijedasa.setField(StandardField.PAGES, "977--982");
         entryWijedasa.setField(StandardField.PMID, "27670948");
         entryWijedasa.setField(new UnknownField("pubmodel"), "Print-Electronic");
@@ -65,7 +64,7 @@ public void setUp() throws InterruptedException {
         entryEndharti.setField(StandardField.JOURNAL, "BMC complementary and alternative medicine");
         entryEndharti.setField(StandardField.KEYWORDS, "CAC; Dendrophtoe pentandra; IL-22; MPO; Proliferation; p53");
         entryEndharti.setField(new UnknownField("nlm-id"), "101088661");
-        entryEndharti.setField(InternalField.OWNER, "NLM");
+        entryEndharti.setField(StandardField.OWNER, "NLM");
         entryEndharti.setField(StandardField.PAGES, "374");
         entryEndharti.setField(StandardField.MONTH, "#sep#");
         entryEndharti.setField(StandardField.PMID, "27670445");
@@ -92,7 +91,7 @@ public void setUp() throws InterruptedException {
         bibEntryIchikawa.setField(StandardField.KEYWORDS, "Animals; Antibodies, Protozoan, blood; Antigens, Protozoan, immunology; Cattle, parasitology; Cattle Diseases, epidemiology, parasitology; Enzyme-Linked Immunosorbent Assay, veterinary; Geography; Humans; Indonesia, epidemiology; Livestock, immunology, parasitology; Meat, parasitology; Protozoan Proteins, immunology; Seroepidemiologic Studies; Swine, parasitology; Swine Diseases, epidemiology, parasitology; Toxoplasma, immunology; Toxoplasmosis, Animal, epidemiology, immunology, parasitology; Cattle; ELISA; Indonesia; Pig; TgGRA7; Toxoplasma gondii");
         bibEntryIchikawa.setField(StandardField.MONTH, "#dec#");
         bibEntryIchikawa.setField(new UnknownField("nlm-id"), "9708549");
-        bibEntryIchikawa.setField(InternalField.OWNER, "NLM");
+        bibEntryIchikawa.setField(StandardField.OWNER, "NLM");
         bibEntryIchikawa.setField(StandardField.PAGES, "484--486");
         bibEntryIchikawa.setField(new UnknownField("pii"), "S1383-5769(15)00124-5");
         bibEntryIchikawa.setField(StandardField.PMID, "26197440");
@@ -117,7 +116,7 @@ public void setUp() throws InterruptedException {
         bibEntrySari.setField(StandardField.PUBSTATE, "ppublish");
         bibEntrySari.setField(new UnknownField("revised"), "2018-12-02");
         bibEntrySari.setField(new UnknownField("nlm-id"), "0266303");
-        bibEntrySari.setField(InternalField.OWNER, "NLM");
+        bibEntrySari.setField(StandardField.OWNER, "NLM");
         bibEntrySari.setField(StandardField.PAGES, "977--985");
         bibEntrySari.setField(StandardField.PMID, "26867355");
         bibEntrySari.setField(new UnknownField("pubmodel"), "Print");
diff --git a/src/test/java/org/jabref/logic/importer/fileformat/BibtexParserTest.java b/src/test/java/org/jabref/logic/importer/fileformat/BibtexParserTest.java
index ed083822907..42c024968ae 100644
--- a/src/test/java/org/jabref/logic/importer/fileformat/BibtexParserTest.java
+++ b/src/test/java/org/jabref/logic/importer/fileformat/BibtexParserTest.java
@@ -485,8 +485,8 @@ void parseRecognizesHeaderButIgnoresEncoding() throws IOException {
         assertEquals(Optional.of("Hawaii International Conference On System Sciences (HICSS)"),
                 entry.getField(StandardField.BOOKTITLE));
         assertEquals(Optional.of("2005"), entry.getField(StandardField.YEAR));
-        assertEquals(Optional.of("oezbek"), entry.getField(InternalField.OWNER));
-        assertEquals(Optional.of("2006.05.29"), entry.getField(InternalField.TIMESTAMP));
+        assertEquals(Optional.of("oezbek"), entry.getField(StandardField.OWNER));
+        assertEquals(Optional.of("2006.05.29"), entry.getField(StandardField.TIMESTAMP));
         assertEquals(Optional.of("http://james.howison.name/publications.html"), entry.getField(StandardField.URL));
     }
 
@@ -513,8 +513,8 @@ void parseRecognizesFormatedEntry() throws IOException {
         assertEquals(Optional.of("Hawaii International Conference On System Sciences (HICSS)"),
                 entry.getField(StandardField.BOOKTITLE));
         assertEquals(Optional.of("2005"), entry.getField(StandardField.YEAR));
-        assertEquals(Optional.of("oezbek"), entry.getField(InternalField.OWNER));
-        assertEquals(Optional.of("2006.05.29"), entry.getField(InternalField.TIMESTAMP));
+        assertEquals(Optional.of("oezbek"), entry.getField(StandardField.OWNER));
+        assertEquals(Optional.of("2006.05.29"), entry.getField(StandardField.TIMESTAMP));
         assertEquals(Optional.of("http://james.howison.name/publications.html"), entry.getField(StandardField.URL));
     }
 
@@ -617,18 +617,6 @@ void parseReturnsEmptyListIfNoEntryExistent() throws IOException {
         assertEquals(0, parsed.size());
     }
 
-    @Test
-    void parseRecognizesDuplicateBibtexKeys() throws IOException {
-        ParserResult result = parser
-                .parse(new StringReader("@article{canh05," + "  author = {Crowston, K. and Annabi, H.},\n"
-                        + "  title = {Title A}}\n" + "@inProceedings{canh05," + "  author={Norton Bar}}"));
-
-        List<String> duplicateKeys = result.getDuplicateKeys();
-
-        assertEquals(1, duplicateKeys.size());
-        assertEquals("canh05", duplicateKeys.get(0));
-    }
-
     @Test
     void parseNotWarnsAboutEntryWithoutBibtexKey() throws IOException {
         BibEntry expected = new BibEntry();
diff --git a/src/test/java/org/jabref/logic/layout/LayoutEntryTest.java b/src/test/java/org/jabref/logic/layout/LayoutEntryTest.java
index 5380dd77fbf..a3013361690 100644
--- a/src/test/java/org/jabref/logic/layout/LayoutEntryTest.java
+++ b/src/test/java/org/jabref/logic/layout/LayoutEntryTest.java
@@ -4,7 +4,6 @@
 import java.io.StringReader;
 
 import org.jabref.model.entry.BibEntry;
-import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.SpecialField;
 import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.entry.field.UnknownField;
@@ -49,13 +48,13 @@ public void setUp() {
         mBTE.setField(new UnknownField("citeulike-linkout-1"), "http://dx.doi.org/10.1145/1554339.1554341");
         mBTE.setField(StandardField.URL, "http://dx.doi.org/10.1145/1554339.1554341");
         mBTE.setField(StandardField.PUBLISHER, "ACM");
-        mBTE.setField(InternalField.TIMESTAMP, "2010.11.11");
+        mBTE.setField(StandardField.TIMESTAMP, "2010.11.11");
         mBTE.setField(StandardField.AUTHOR, "Chaudhuri, Avik");
         mBTE.setField(StandardField.TITLE, "Language-based security on Android");
         mBTE.setField(StandardField.ADDRESS, "New York, NY, USA");
         mBTE.setField(SpecialField.PRIORITY, "2");
         mBTE.setField(StandardField.ISBN, "978-1-60558-645-8");
-        mBTE.setField(InternalField.OWNER, "Arne");
+        mBTE.setField(StandardField.OWNER, "Arne");
         mBTE.setField(StandardField.YEAR, "2009");
         mBTE.setField(new UnknownField("citeulike-linkout-0"), "http://portal.acm.org/citation.cfm?id=1554339.1554341");
         mBTE.setField(StandardField.DOI, "10.1145/1554339.1554341");
diff --git a/src/test/java/org/jabref/logic/xmp/XmpUtilWriterTest.java b/src/test/java/org/jabref/logic/xmp/XmpUtilWriterTest.java
index 4374f76b69c..b2e911e1d3b 100644
--- a/src/test/java/org/jabref/logic/xmp/XmpUtilWriterTest.java
+++ b/src/test/java/org/jabref/logic/xmp/XmpUtilWriterTest.java
@@ -10,7 +10,6 @@
 
 import org.jabref.model.entry.BibEntry;
 import org.jabref.model.entry.Month;
-import org.jabref.model.entry.field.InternalField;
 import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.entry.types.StandardEntryType;
 
@@ -47,10 +46,10 @@ private void initBibEntries() {
         olly2018.setField(StandardField.COMMENT, "COMMENT");
         olly2018.setField(StandardField.DOI, "10/3212.3123");
         olly2018.setField(StandardField.FILE, ":article_dublinCore.pdf:PDF");
-        olly2018.setField(InternalField.GROUPS, "NO");
+        olly2018.setField(StandardField.GROUPS, "NO");
         olly2018.setField(StandardField.HOWPUBLISHED, "online");
         olly2018.setField(StandardField.KEYWORDS, "k1, k2");
-        olly2018.setField(InternalField.OWNER, "me");
+        olly2018.setField(StandardField.OWNER, "me");
         olly2018.setField(StandardField.REVIEW, "review");
         olly2018.setField(StandardField.URL, "https://www.olly2018.edu");
 
@@ -60,7 +59,7 @@ private void initBibEntries() {
         toral2006.setField(StandardField.BOOKTITLE, "Proceedings of EACL");
         toral2006.setField(StandardField.PAGES, "56--61");
         toral2006.setField(StandardField.EPRINTTYPE, "asdf");
-        toral2006.setField(InternalField.OWNER, "Ich");
+        toral2006.setField(StandardField.OWNER, "Ich");
         toral2006.setField(StandardField.URL, "www.url.de");
 
         vapnik2000 = new BibEntry(StandardEntryType.Book);
@@ -69,7 +68,7 @@ private void initBibEntries() {
         vapnik2000.setField(StandardField.PUBLISHER, "Springer Science + Business Media");
         vapnik2000.setField(StandardField.AUTHOR, "Vladimir N. Vapnik");
         vapnik2000.setField(StandardField.DOI, "10.1007/978-1-4757-3264-1");
-        vapnik2000.setField(InternalField.OWNER, "Ich");
+        vapnik2000.setField(StandardField.OWNER, "Ich");
     }
 
     /**
diff --git a/src/test/java/org/jabref/migrations/ConvertLegacyExplicitGroupsTest.java b/src/test/java/org/jabref/migrations/ConvertLegacyExplicitGroupsTest.java
index cdbe1a59f68..8e6b6013a32 100644
--- a/src/test/java/org/jabref/migrations/ConvertLegacyExplicitGroupsTest.java
+++ b/src/test/java/org/jabref/migrations/ConvertLegacyExplicitGroupsTest.java
@@ -5,7 +5,7 @@
 
 import org.jabref.logic.importer.ParserResult;
 import org.jabref.model.entry.BibEntry;
-import org.jabref.model.entry.field.InternalField;
+import org.jabref.model.entry.field.StandardField;
 import org.jabref.model.groups.AllEntriesGroup;
 import org.jabref.model.groups.ExplicitGroup;
 import org.jabref.model.groups.GroupHierarchyType;
@@ -16,14 +16,14 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-public class ConvertLegacyExplicitGroupsTest {
+class ConvertLegacyExplicitGroupsTest {
 
     private PostOpenMigration action;
     private BibEntry entry;
     private ExplicitGroup group;
 
     @BeforeEach
-    public void setUp() throws Exception {
+    void setUp() throws Exception {
         action = new ConvertLegacyExplicitGroups();
 
         entry = new BibEntry();
@@ -33,16 +33,16 @@ public void setUp() throws Exception {
     }
 
     @Test
-    public void performActionWritesGroupMembershipInEntry() throws Exception {
+    void performActionWritesGroupMembershipInEntry() throws Exception {
         ParserResult parserResult = generateParserResult(GroupTreeNode.fromGroup(group));
 
         action.performMigration(parserResult);
 
-        assertEquals(Optional.of("TestGroup"), entry.getField(InternalField.GROUPS));
+        assertEquals(Optional.of("TestGroup"), entry.getField(StandardField.GROUPS));
     }
 
     @Test
-    public void performActionClearsLegacyKeys() throws Exception {
+    void performActionClearsLegacyKeys() throws Exception {
         ParserResult parserResult = generateParserResult(GroupTreeNode.fromGroup(group));
 
         action.performMigration(parserResult);
@@ -51,7 +51,7 @@ public void performActionClearsLegacyKeys() throws Exception {
     }
 
     @Test
-    public void performActionWritesGroupMembershipInEntryForComplexGroupTree() throws Exception {
+    void performActionWritesGroupMembershipInEntryForComplexGroupTree() throws Exception {
         GroupTreeNode root = GroupTreeNode.fromGroup(new AllEntriesGroup(""));
         root.addSubgroup(new ExplicitGroup("TestGroup2", GroupHierarchyType.INCLUDING, ','));
         root.addSubgroup(group);
@@ -59,7 +59,7 @@ public void performActionWritesGroupMembershipInEntryForComplexGroupTree() throw
 
         action.performMigration(parserResult);
 
-        assertEquals(Optional.of("TestGroup"), entry.getField(InternalField.GROUPS));
+        assertEquals(Optional.of("TestGroup"), entry.getField(StandardField.GROUPS));
     }
 
     private ParserResult generateParserResult(GroupTreeNode groupRoot) {
diff --git a/src/test/java/org/jabref/model/database/BibDatabaseModeDetectionTest.java b/src/test/java/org/jabref/model/database/BibDatabaseModeDetectionTest.java
index 92e001e3604..30937e8235e 100644
--- a/src/test/java/org/jabref/model/database/BibDatabaseModeDetectionTest.java
+++ b/src/test/java/org/jabref/model/database/BibDatabaseModeDetectionTest.java
@@ -1,7 +1,7 @@
 package org.jabref.model.database;
 
 import java.util.Arrays;
-import java.util.Collection;
+import java.util.List;
 
 import org.jabref.model.entry.BibEntry;
 import org.jabref.model.entry.field.StandardField;
@@ -19,18 +19,18 @@ public class BibDatabaseModeDetectionTest {
 
     @Test
     public void detectBiblatex() {
-        Collection<BibEntry> entries = Arrays.asList(new BibEntry(StandardEntryType.MvBook));
+        List<BibEntry> entries = Arrays.asList(new BibEntry(StandardEntryType.MvBook));
 
-        assertEquals(BibDatabaseMode.BIBLATEX, BibDatabaseModeDetection.inferMode(BibDatabases.createDatabase(entries)));
+        assertEquals(BibDatabaseMode.BIBLATEX, BibDatabaseModeDetection.inferMode(new BibDatabase(entries)));
     }
 
     @Test
     public void detectUndistinguishableAsBibtex() {
         BibEntry entry = new BibEntry(StandardEntryType.Article);
         entry.setField(StandardField.TITLE, "My cool paper");
-        Collection<BibEntry> entries = Arrays.asList(entry);
+        List<BibEntry> entries = Arrays.asList(entry);
 
-        assertEquals(BibDatabaseMode.BIBTEX, BibDatabaseModeDetection.inferMode(BibDatabases.createDatabase(entries)));
+        assertEquals(BibDatabaseMode.BIBTEX, BibDatabaseModeDetection.inferMode(new BibDatabase(entries)));
     }
 
     @Test
@@ -39,17 +39,17 @@ public void detectMixedModeAsBiblatex() {
         bibtex.setField(StandardField.JOURNAL, "IEEE Trans. Services Computing");
         BibEntry biblatex = new BibEntry(StandardEntryType.Article);
         biblatex.setField(StandardField.TRANSLATOR, "Stefan Kolb");
-        Collection<BibEntry> entries = Arrays.asList(bibtex, biblatex);
+        List<BibEntry> entries = Arrays.asList(bibtex, biblatex);
 
-        assertEquals(BibDatabaseMode.BIBTEX, BibDatabaseModeDetection.inferMode(BibDatabases.createDatabase(entries)));
+        assertEquals(BibDatabaseMode.BIBTEX, BibDatabaseModeDetection.inferMode(new BibDatabase(entries)));
     }
 
     @Test
     public void detectUnknownTypeAsBibtex() {
         BibEntry entry = new BibEntry(UNKNOWN_TYPE);
-        Collection<BibEntry> entries = Arrays.asList(entry);
+        List<BibEntry> entries = Arrays.asList(entry);
 
-        assertEquals(BibDatabaseMode.BIBTEX, BibDatabaseModeDetection.inferMode(BibDatabases.createDatabase(entries)));
+        assertEquals(BibDatabaseMode.BIBTEX, BibDatabaseModeDetection.inferMode(new BibDatabase(entries)));
     }
 
     @Test
@@ -57,9 +57,9 @@ public void ignoreUnknownTypesForBibtexDecision() {
         BibEntry custom = new BibEntry(UNKNOWN_TYPE);
         BibEntry bibtex = new BibEntry(StandardEntryType.Article);
         BibEntry biblatex = new BibEntry(StandardEntryType.Article);
-        Collection<BibEntry> entries = Arrays.asList(custom, bibtex, biblatex);
+        List<BibEntry> entries = Arrays.asList(custom, bibtex, biblatex);
 
-        assertEquals(BibDatabaseMode.BIBTEX, BibDatabaseModeDetection.inferMode(BibDatabases.createDatabase(entries)));
+        assertEquals(BibDatabaseMode.BIBTEX, BibDatabaseModeDetection.inferMode(new BibDatabase(entries)));
     }
 
     @Test
@@ -67,8 +67,8 @@ public void ignoreUnknownTypesForBiblatexDecision() {
         BibEntry custom = new BibEntry(UNKNOWN_TYPE);
         BibEntry bibtex = new BibEntry(StandardEntryType.Article);
         BibEntry biblatex = new BibEntry(StandardEntryType.MvBook);
-        Collection<BibEntry> entries = Arrays.asList(custom, bibtex, biblatex);
+        List<BibEntry> entries = Arrays.asList(custom, bibtex, biblatex);
 
-        assertEquals(BibDatabaseMode.BIBLATEX, BibDatabaseModeDetection.inferMode(BibDatabases.createDatabase(entries)));
+        assertEquals(BibDatabaseMode.BIBLATEX, BibDatabaseModeDetection.inferMode(new BibDatabase(entries)));
     }
 }
diff --git a/src/test/java/org/jabref/model/database/BibDatabaseTest.java b/src/test/java/org/jabref/model/database/BibDatabaseTest.java
index 5f417a8c486..26dbab89bef 100644
--- a/src/test/java/org/jabref/model/database/BibDatabaseTest.java
+++ b/src/test/java/org/jabref/model/database/BibDatabaseTest.java
@@ -53,13 +53,13 @@ void containsEntryIdFindsEntry() {
     }
 
     @Test
-    void insertEntryWithSameIdThrowsException() {
+    void insertEntryWithSameIdDoesNotThrowException() {
         BibEntry entry0 = new BibEntry();
         database.insertEntry(entry0);
 
         BibEntry entry1 = new BibEntry();
         entry1.setId(entry0.getId());
-        assertThrows(KeyCollisionException.class, () -> database.insertEntry(entry1));
+        database.insertEntry(entry1);
     }
 
     @Test
diff --git a/src/test/java/org/jabref/model/groups/ExplicitGroupTest.java b/src/test/java/org/jabref/model/groups/ExplicitGroupTest.java
index cdee1413af0..e629b7dfc76 100644
--- a/src/test/java/org/jabref/model/groups/ExplicitGroupTest.java
+++ b/src/test/java/org/jabref/model/groups/ExplicitGroupTest.java
@@ -3,7 +3,7 @@
 import java.util.Optional;
 
 import org.jabref.model.entry.BibEntry;
-import org.jabref.model.entry.field.InternalField;
+import org.jabref.model.entry.field.StandardField;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -12,7 +12,7 @@
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
-public class ExplicitGroupTest {
+class ExplicitGroupTest {
 
     private ExplicitGroup group;
     private ExplicitGroup group2;
@@ -20,75 +20,75 @@ public class ExplicitGroupTest {
     private BibEntry entry;
 
     @BeforeEach
-    public void setUp() {
+    void setUp() {
         group = new ExplicitGroup("myExplicitGroup", GroupHierarchyType.INDEPENDENT, ',');
         group2 = new ExplicitGroup("myExplicitGroup2", GroupHierarchyType.INCLUDING, ',');
         entry = new BibEntry();
     }
 
     @Test
-    public void addSingleGroupToEmptyBibEntryChangesGroupsField() {
+    void addSingleGroupToEmptyBibEntryChangesGroupsField() {
         group.add(entry);
-        assertEquals(Optional.of("myExplicitGroup"), entry.getField(InternalField.GROUPS));
+        assertEquals(Optional.of("myExplicitGroup"), entry.getField(StandardField.GROUPS));
     }
 
     @Test
-    public void addSingleGroupToNonemptyBibEntryAppendsToGroupsField() {
-        entry.setField(InternalField.GROUPS, "some thing");
+    void addSingleGroupToNonemptyBibEntryAppendsToGroupsField() {
+        entry.setField(StandardField.GROUPS, "some thing");
         group.add(entry);
-        assertEquals(Optional.of("some thing, myExplicitGroup"), entry.getField(InternalField.GROUPS));
+        assertEquals(Optional.of("some thing, myExplicitGroup"), entry.getField(StandardField.GROUPS));
     }
 
     @Test
-    public void addTwoGroupsToBibEntryChangesGroupsField() {
+    void addTwoGroupsToBibEntryChangesGroupsField() {
         group.add(entry);
         group2.add(entry);
-        assertEquals(Optional.of("myExplicitGroup, myExplicitGroup2"), entry.getField(InternalField.GROUPS));
+        assertEquals(Optional.of("myExplicitGroup, myExplicitGroup2"), entry.getField(StandardField.GROUPS));
     }
 
     @Test
-    public void addDuplicateGroupDoesNotChangeGroupsField() throws Exception {
-        entry.setField(InternalField.GROUPS, "myExplicitGroup");
+    void addDuplicateGroupDoesNotChangeGroupsField() throws Exception {
+        entry.setField(StandardField.GROUPS, "myExplicitGroup");
         group.add(entry);
-        assertEquals(Optional.of("myExplicitGroup"), entry.getField(InternalField.GROUPS));
+        assertEquals(Optional.of("myExplicitGroup"), entry.getField(StandardField.GROUPS));
     }
 
     @Test
-    // For https://github.com/JabRef/jabref/issues/2334
-    public void removeDoesNotChangeFieldIfContainsNameAsPart() throws Exception {
-        entry.setField(InternalField.GROUPS, "myExplicitGroup_alternative");
+        // For https://github.com/JabRef/jabref/issues/2334
+    void removeDoesNotChangeFieldIfContainsNameAsPart() throws Exception {
+        entry.setField(StandardField.GROUPS, "myExplicitGroup_alternative");
         group.remove(entry);
-        assertEquals(Optional.of("myExplicitGroup_alternative"), entry.getField(InternalField.GROUPS));
+        assertEquals(Optional.of("myExplicitGroup_alternative"), entry.getField(StandardField.GROUPS));
     }
 
     @Test
-    // For https://github.com/JabRef/jabref/issues/2334
-    public void removeDoesNotChangeFieldIfContainsNameAsWord() throws Exception {
-        entry.setField(InternalField.GROUPS, "myExplicitGroup alternative");
+        // For https://github.com/JabRef/jabref/issues/2334
+    void removeDoesNotChangeFieldIfContainsNameAsWord() throws Exception {
+        entry.setField(StandardField.GROUPS, "myExplicitGroup alternative");
         group.remove(entry);
 
-        assertEquals(Optional.of("myExplicitGroup alternative"), entry.getField(InternalField.GROUPS));
+        assertEquals(Optional.of("myExplicitGroup alternative"), entry.getField(StandardField.GROUPS));
     }
 
     @Test
-    // For https://github.com/JabRef/jabref/issues/1873
-    public void containsOnlyMatchesCompletePhraseWithWhitespace() throws Exception {
-        entry.setField(InternalField.GROUPS, "myExplicitGroup b");
+        // For https://github.com/JabRef/jabref/issues/1873
+    void containsOnlyMatchesCompletePhraseWithWhitespace() throws Exception {
+        entry.setField(StandardField.GROUPS, "myExplicitGroup b");
         assertFalse(group.contains(entry));
     }
 
     @Test
-    // For https://github.com/JabRef/jabref/issues/1873
-    public void containsOnlyMatchesCompletePhraseWithSlash() throws Exception {
-        entry.setField(InternalField.GROUPS, "myExplicitGroup/b");
+        // For https://github.com/JabRef/jabref/issues/1873
+    void containsOnlyMatchesCompletePhraseWithSlash() throws Exception {
+        entry.setField(StandardField.GROUPS, "myExplicitGroup/b");
 
         assertFalse(group.contains(entry));
     }
 
     @Test
-    // For https://github.com/JabRef/jabref/issues/2394
-    public void containsMatchesPhraseWithBrackets() throws Exception {
-        entry.setField(InternalField.GROUPS, "[aa] Subgroup1");
+        // For https://github.com/JabRef/jabref/issues/2394
+    void containsMatchesPhraseWithBrackets() throws Exception {
+        entry.setField(StandardField.GROUPS, "[aa] Subgroup1");
         ExplicitGroup explicitGroup = new ExplicitGroup("[aa] Subgroup1", GroupHierarchyType.INCLUDING, ',');
 
         assertTrue(explicitGroup.contains(entry));