diff --git a/src/main/java/com/sitepark/ies/extension/api/ConfigurationContext.java b/src/main/java/com/sitepark/ies/extension/api/ConfigurationContext.java
index b855b3f..6c39ce4 100644
--- a/src/main/java/com/sitepark/ies/extension/api/ConfigurationContext.java
+++ b/src/main/java/com/sitepark/ies/extension/api/ConfigurationContext.java
@@ -11,7 +11,7 @@ public class ConfigurationContext {
 
 	private final List<Module> injectionModuleList = new ArrayList<>();
 
-	private ClassFinder classFinder = null;
+	private ClassFinder classFinder;
 
 	private final List<EventListener> servletContextEventListenerList = new ArrayList<>();
 
@@ -23,7 +23,7 @@ public void addServletContextEventListener(EventListener listener) {
 	}
 
 	public List<EventListener> getServletContextEventListener() {
-		return this.servletContextEventListenerList;
+		return Collections.unmodifiableList(this.servletContextEventListenerList);
 	}
 
 	public void addInjectionModule(Module injectionModule) {
diff --git a/src/main/java/com/sitepark/ies/extension/api/exeptions/InvalidExtensionClass.java b/src/main/java/com/sitepark/ies/extension/api/exeptions/InvalidExtensionClass.java
index 92981dd..c427bc6 100644
--- a/src/main/java/com/sitepark/ies/extension/api/exeptions/InvalidExtensionClass.java
+++ b/src/main/java/com/sitepark/ies/extension/api/exeptions/InvalidExtensionClass.java
@@ -4,16 +4,18 @@
 
 public class InvalidExtensionClass extends ExtensionException {
 
-	private Class<? extends Extension> extensionClass;
+	private final Class<? extends Extension> extensionClass;
 
 	private static final long serialVersionUID = 1L;
 
 	public InvalidExtensionClass(Class<? extends Extension> extensionClass, String message) {
 		super(message);
+		this.extensionClass = extensionClass;
 	}
 
 	public InvalidExtensionClass(Class<? extends Extension> extensionClass, String message, Throwable t) {
 		super(message, t);
+		this.extensionClass = extensionClass;
 	}
 
 	public Class<? extends Extension> getExtensionClass() {