diff --git a/CHANGELOG.md b/CHANGELOG.md
index edf14cabc..7723c4b0a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 Changes to Calva.
 
 ## [Unreleased]
+- Maintenance: [Begin work on enabling strictNullChecks in the TypeScript config.](https://github.com/BetterThanTomorrow/calva/pull/1568)
 
 ## [2.0.252] - 2022-03-05
 - Fix: [Tab doesn't work in snippet mode](https://github.com/BetterThanTomorrow/calva/pull/1580)
diff --git a/package.json b/package.json
index 1e15b72c9..2e6dc8d2b 100644
--- a/package.json
+++ b/package.json
@@ -2600,7 +2600,8 @@
         "clean": "rimraf ./out && rimraf ./tsconfig.tsbuildinfo && rimraf ./cljs-out",
         "compile-cljs": "npx shadow-cljs compile :calva-lib :test",
         "prewatch": "npm i && npm run clean && npm run update-grammar && npm run compile-cljs",
-        "watch": "npx tsc -watch -p ./tsconfig.json",
+        "watch": "npx tsc --watch --project ./tsconfig.json",
+        "watch-with-strict-nulls": "npx tsc --watch --project ./tsconfig.json --strictNullChecks",
         "release-cljs": "npx shadow-cljs release :calva-lib :test",
         "update-grammar": "node ./src/calva-fmt/update-grammar.js ./src/calva-fmt/atom-language-clojure/grammars/clojure.cson clojure.tmLanguage.json",
         "release": "npm i && npm run clean && npm run update-grammar && npm run release-cljs && webpack --mode production",
@@ -2687,4 +2688,4 @@
         "webpack": "^5.27.1",
         "webpack-cli": "^4.5.0"
     }
-}
+}
\ No newline at end of file
diff --git a/src/calva-fmt/src/format.ts b/src/calva-fmt/src/format.ts
index 000dfe3fc..346e519a8 100644
--- a/src/calva-fmt/src/format.ts
+++ b/src/calva-fmt/src/format.ts
@@ -3,9 +3,9 @@ import * as config from './config';
 import * as outputWindow from '../../results-output/results-doc';
 import {
     getIndent,
-    getDocument,
     getDocumentOffset,
     MirroredDocument,
+    mustGetDocument,
 } from '../../doc-mirror/index';
 import {
     formatTextAtRange,
@@ -15,15 +15,16 @@ import {
     cljify,
     jsify,
 } from '../../../out/cljs-lib/cljs-lib';
+import * as util from '../../utilities';
 
 export async function indentPosition(
     position: vscode.Position,
     document: vscode.TextDocument
 ) {
-    const editor = vscode.window.activeTextEditor;
+    const editor = util.mustGetActiveTextEditor();
     const pos = new vscode.Position(position.line, 0);
     const indent = getIndent(
-        getDocument(document).model.lineInputModel,
+        mustGetDocument(document).model.lineInputModel,
         getDocumentOffset(document, position),
         await config.getConfig()
     );
@@ -55,7 +56,7 @@ export async function formatRangeEdits(
     range: vscode.Range
 ): Promise<vscode.TextEdit[]> {
     const text: string = document.getText(range);
-    const mirroredDoc: MirroredDocument = getDocument(document);
+    const mirroredDoc: MirroredDocument = mustGetDocument(document);
     const startIndex = document.offsetAt(range.start);
     const endIndex = document.offsetAt(range.end);
     const cursor = mirroredDoc.getTokenCursor(startIndex);
@@ -90,7 +91,7 @@ export async function formatPositionInfo(
     const doc: vscode.TextDocument = editor.document;
     const pos: vscode.Position = editor.selection.active;
     const index = doc.offsetAt(pos);
-    const mirroredDoc: MirroredDocument = getDocument(doc);
+    const mirroredDoc: MirroredDocument = mustGetDocument(doc);
     const cursor = mirroredDoc.getTokenCursor(index);
     const formatDepth = extraConfig['format-depth']
         ? extraConfig['format-depth']
diff --git a/src/calva-fmt/src/providers/ontype_formatter.ts b/src/calva-fmt/src/providers/ontype_formatter.ts
index cf2d54c36..ba22fc94f 100644
--- a/src/calva-fmt/src/providers/ontype_formatter.ts
+++ b/src/calva-fmt/src/providers/ontype_formatter.ts
@@ -4,6 +4,7 @@ import * as docMirror from '../../../doc-mirror/index';
 import { EditableDocument } from '../../../cursor-doc/model';
 import * as paredit from '../../../cursor-doc/paredit';
 import { getConfig } from '../../../config';
+import * as util from '../../../utilities';
 
 export class FormatOnTypeEditProvider
     implements vscode.OnTypeFormattingEditProvider
@@ -14,7 +15,6 @@ export class FormatOnTypeEditProvider
         ch: string,
         _options
     ): Promise<vscode.TextEdit[]> {
-        const editor = vscode.window.activeTextEditor;
         let keyMap = vscode.workspace
             .getConfiguration()
             .get('calva.paredit.defaultKeyMap');
@@ -24,7 +24,8 @@ export class FormatOnTypeEditProvider
                 keyMap === 'strict' &&
                 getConfig().strictPreventUnmatchedClosingBracket
             ) {
-                const mDoc: EditableDocument = docMirror.getDocument(document);
+                const mDoc: EditableDocument =
+                    docMirror.mustGetDocument(document);
                 const tokenCursor = mDoc.getTokenCursor();
                 if (tokenCursor.withinComment()) {
                     return null;
@@ -37,6 +38,7 @@ export class FormatOnTypeEditProvider
                 return null;
             }
         }
+        const editor = util.mustGetActiveTextEditor();
 
         const pos = editor.selection.active;
         if (
diff --git a/src/clojuredocs.ts b/src/clojuredocs.ts
index e17f7f13d..69a19aa05 100644
--- a/src/clojuredocs.ts
+++ b/src/clojuredocs.ts
@@ -63,7 +63,7 @@ export function printTextToRichCommentCommand(args: { [x: string]: string }) {
 
 function printTextToRichComment(text: string, position?: number) {
     const doc = util.getDocument({});
-    const mirrorDoc = docMirror.getDocument(doc);
+    const mirrorDoc = docMirror.mustGetDocument(doc);
     paredit.addRichComment(
         mirrorDoc,
         position ? position : mirrorDoc.selection.active,
@@ -183,7 +183,7 @@ async function clojureDocsLookup(
     p?: vscode.Position
 ): Promise<DocsEntry> {
     const doc = d ? d : util.getDocument({});
-    const position = p ? p : vscode.window.activeTextEditor.selection.active;
+    const position = p ? p : util.mustGetActiveTextEditor().selection.active;
     const symbol = util.getWordAtPosition(doc, position);
     const ns = namespace.getNamespace(doc);
     const session = replSession.getSession(util.getFileType(doc));
diff --git a/src/connector.ts b/src/connector.ts
index c52256635..ff8fd40e8 100644
--- a/src/connector.ts
+++ b/src/connector.ts
@@ -837,7 +837,7 @@ export default {
             setStateValue('cljc', newSession);
             if (
                 outputWindow.isResultsDoc(
-                    vscode.window.activeTextEditor.document
+                    util.mustGetActiveTextEditor().document
                 )
             ) {
                 outputWindow.setSession(newSession, undefined);
diff --git a/src/custom-snippets.ts b/src/custom-snippets.ts
index b47e573fb..1b423f00d 100644
--- a/src/custom-snippets.ts
+++ b/src/custom-snippets.ts
@@ -15,7 +15,7 @@ async function evaluateCustomCodeSnippetCommand(codeOrKey?: string) {
 }
 
 async function evaluateCodeOrKey(codeOrKey?: string) {
-    const editor = vscode.window.activeTextEditor;
+    const editor = util.mustGetActiveTextEditor();
     const currentLine = editor.selection.active.line;
     const currentColumn = editor.selection.active.character;
     const currentFilename = editor.document.fileName;
diff --git a/src/debugger/calva-debug.ts b/src/debugger/calva-debug.ts
index d74a6680b..c7beced36 100644
--- a/src/debugger/calva-debug.ts
+++ b/src/debugger/calva-debug.ts
@@ -287,7 +287,7 @@ class CalvaDebugSession extends LoggingDebugSession {
             new Position(positionLine, positionColumn)
         );
         const tokenCursor = docMirror
-            .getDocument(document)
+            .mustGetDocument(document)
             .getTokenCursor(offset);
 
         try {
diff --git a/src/debugger/decorations.ts b/src/debugger/decorations.ts
index 37a60c186..e1cc7f057 100644
--- a/src/debugger/decorations.ts
+++ b/src/debugger/decorations.ts
@@ -144,7 +144,7 @@ function triggerUpdateAndRenderDecorations() {
         timeout = undefined;
     }
     if (enabled) {
-        const editor = vscode.window.activeTextEditor;
+        const editor = util.getActiveTextEditor();
         if (editor) {
             timeout = setTimeout(() => {
                 const cljSession = replSession.getSession('clj');
@@ -166,7 +166,7 @@ function activate() {
     });
 
     vscode.workspace.onDidChangeTextDocument((event) => {
-        const activeEditor = vscode.window.activeTextEditor;
+        const activeEditor = util.getActiveTextEditor();
         if (
             activeEditor &&
             event.document === activeEditor.document &&
diff --git a/src/doc-mirror/index.ts b/src/doc-mirror/index.ts
index abd656b5a..ffe3bc0a9 100644
--- a/src/doc-mirror/index.ts
+++ b/src/doc-mirror/index.ts
@@ -11,6 +11,7 @@ import {
     LineInputModel,
     ModelEditSelection,
 } from '../cursor-doc/model';
+import { isUndefined } from 'lodash';
 
 const documents = new Map<vscode.TextDocument, MirroredDocument>();
 
@@ -28,7 +29,7 @@ export class DocumentModel implements EditableModel {
         modelEdits: ModelEdit[],
         options: ModelEditOptions
     ): Thenable<boolean> {
-        const editor = vscode.window.activeTextEditor,
+        const editor = utilities.mustGetActiveTextEditor(),
             undoStopBefore = !!options.undoStopBefore;
         return editor
             .edit(
@@ -84,7 +85,7 @@ export class DocumentModel implements EditableModel {
         oldSelection?: [number, number],
         newSelection?: [number, number]
     ) {
-        const editor = vscode.window.activeTextEditor,
+        const editor = utilities.mustGetActiveTextEditor(),
             document = editor.document;
         builder.insert(document.positionAt(offset), text);
     }
@@ -97,7 +98,7 @@ export class DocumentModel implements EditableModel {
         oldSelection?: [number, number],
         newSelection?: [number, number]
     ) {
-        const editor = vscode.window.activeTextEditor,
+        const editor = utilities.mustGetActiveTextEditor(),
             document = editor.document,
             range = new vscode.Range(
                 document.positionAt(start),
@@ -113,7 +114,7 @@ export class DocumentModel implements EditableModel {
         oldSelection?: [number, number],
         newSelection?: [number, number]
     ) {
-        const editor = vscode.window.activeTextEditor,
+        const editor = utilities.mustGetActiveTextEditor(),
             document = editor.document,
             range = new vscode.Range(
                 document.positionAt(offset),
@@ -143,13 +144,13 @@ export class MirroredDocument implements EditableDocument {
 
     get selectionLeft(): number {
         return this.document.offsetAt(
-            vscode.window.activeTextEditor.selection.anchor
+            utilities.mustGetActiveTextEditor().selection.anchor
         );
     }
 
     get selectionRight(): number {
         return this.document.offsetAt(
-            vscode.window.activeTextEditor.selection.active
+            utilities.mustGetActiveTextEditor().selection.active
         );
     }
 
@@ -165,7 +166,7 @@ export class MirroredDocument implements EditableDocument {
     }
 
     public insertString(text: string) {
-        const editor = vscode.window.activeTextEditor,
+        const editor = utilities.mustGetActiveTextEditor(),
             selection = editor.selection,
             wsEdit = new vscode.WorkspaceEdit(),
             edit = vscode.TextEdit.insert(
@@ -179,7 +180,7 @@ export class MirroredDocument implements EditableDocument {
     }
 
     set selection(selection: ModelEditSelection) {
-        const editor = vscode.window.activeTextEditor,
+        const editor = utilities.mustGetActiveTextEditor(),
             document = editor.document,
             anchor = document.positionAt(selection.anchor),
             active = document.positionAt(selection.active);
@@ -192,7 +193,7 @@ export class MirroredDocument implements EditableDocument {
     }
 
     public getSelectionText() {
-        const editor = vscode.window.activeTextEditor,
+        const editor = utilities.mustGetActiveTextEditor(),
             selection = editor.selection;
         return this.document.getText(selection);
     }
@@ -241,11 +242,21 @@ export function getDocument(doc: vscode.TextDocument) {
     return documents.get(doc);
 }
 
+export function mustGetDocument(doc: vscode.TextDocument) {
+    const mirrorDoc = documents.get(doc);
+
+    if (isUndefined(mirrorDoc)) {
+        throw new Error('Missing mirror document!');
+    }
+
+    return mirrorDoc;
+}
+
 export function getDocumentOffset(
     doc: vscode.TextDocument,
     position: vscode.Position
 ) {
-    const model = getDocument(doc).model;
+    const model = mustGetDocument(doc).model;
     return model.getOffsetForLine(position.line) + position.character;
 }
 
diff --git a/src/edit.ts b/src/edit.ts
index 87394eef2..0599a71b1 100644
--- a/src/edit.ts
+++ b/src/edit.ts
@@ -7,9 +7,9 @@ import * as docMirror from './doc-mirror/index';
 export function continueCommentCommand() {
     const document = util.getDocument({});
     if (document && document.languageId === 'clojure') {
-        const editor = vscode.window.activeTextEditor;
+        const editor = util.mustGetActiveTextEditor();
         const position = editor.selection.active;
-        const cursor = docMirror.getDocument(document).getTokenCursor();
+        const cursor = docMirror.mustGetDocument(document).getTokenCursor();
         if (cursor.getToken().type !== 'comment') {
             if (cursor.getPrevToken().type === 'comment') {
                 cursor.previous();
diff --git a/src/evaluate.ts b/src/evaluate.ts
index f3813de5e..89da492e0 100644
--- a/src/evaluate.ts
+++ b/src/evaluate.ts
@@ -91,7 +91,7 @@ async function evaluateCode(
     const filePath = options.filePath;
     const session: NReplSession = options.session;
     const ns = options.ns;
-    const editor = vscode.window.activeTextEditor;
+    const editor = util.mustGetActiveTextEditor();
     let result = null;
 
     if (code.length > 0) {
@@ -259,7 +259,7 @@ async function evaluateSelection(document = {}, options) {
     ) => [vscode.Selection, string] = options.selectionFn;
 
     if (getStateValue('connected')) {
-        const editor = vscode.window.activeTextEditor;
+        const editor = util.mustGetActiveTextEditor();
         state.analytics().logEvent('Evaluation', 'selectionFn').send();
         const selection = selectionFn(editor);
         const codeSelection: vscode.Selection = selection[0];
diff --git a/src/extension-test/integration/suite/extension-test.ts b/src/extension-test/integration/suite/extension-test.ts
index c52fe1a0b..dd7fb84ff 100644
--- a/src/extension-test/integration/suite/extension-test.ts
+++ b/src/extension-test/integration/suite/extension-test.ts
@@ -12,7 +12,7 @@ import * as vscode from 'vscode';
 // import * as myExtension from '../extension';
 import * as outputWindow from '../../../results-output/results-doc';
 import { commands } from 'vscode';
-import { getDocument } from '../../../doc-mirror';
+import { mustGetDocument } from '../../../doc-mirror';
 
 void vscode.window.showInformationMessage('Tests running. Yay!');
 
@@ -85,7 +85,7 @@ suite('Extension Test Suite', () => {
         await sleep(500); // wait a little longer for repl output to be done
         console.log('connected to repl');
 
-        const resultsDoc = getDocument(await outputWindow.openResultsDoc());
+        const resultsDoc = mustGetDocument(await outputWindow.openResultsDoc());
 
         // focus the clojure file
         await vscode.workspace.openTextDocument(testUri).then((doc) =>
diff --git a/src/file-switcher/file-switcher.ts b/src/file-switcher/file-switcher.ts
index 649a2ef56..8aa32dbf4 100644
--- a/src/file-switcher/file-switcher.ts
+++ b/src/file-switcher/file-switcher.ts
@@ -2,6 +2,7 @@ import * as vscode from 'vscode';
 import * as path from 'path';
 import * as util from './util';
 import * as projectRoot from '../project-root';
+import { mustGetActiveTextEditor } from '../utilities';
 
 function openFile(file) {
     return vscode.workspace
@@ -39,7 +40,7 @@ function askToCreateANewFile(dir, file) {
 }
 
 export async function toggleBetweenImplAndTest() {
-    const activeFile = vscode.window.activeTextEditor;
+    const activeFile = mustGetActiveTextEditor();
     const openedFilename = activeFile.document.fileName;
 
     const projectRootUri = await projectRoot.getProjectRootUri();
diff --git a/src/highlight/src/extension.ts b/src/highlight/src/extension.ts
index 8491b0a62..ffe5ad24c 100755
--- a/src/highlight/src/extension.ts
+++ b/src/highlight/src/extension.ts
@@ -5,6 +5,7 @@ import { isArray } from 'util';
 import * as docMirror from '../../doc-mirror/index';
 import { Token, validPair } from '../../cursor-doc/clojure-lexer';
 import { LispTokenCursor } from '../../cursor-doc/token-cursor';
+import { getActiveTextEditor, mustGetActiveTextEditor } from '../../utilities';
 
 type StackItem = {
     char: string;
@@ -264,7 +265,7 @@ function updateRainbowBrackets() {
     }
 
     const doc = activeEditor.document,
-        mirrorDoc = docMirror.getDocument(doc),
+        mirrorDoc = docMirror.mustGetDocument(doc),
         rainbow = rainbowTypes.map(() => []),
         rainbowGuides = rainbowTypes.map(() => []),
         misplaced = [],
@@ -540,7 +541,7 @@ function decorateGuide(
 
 function decorateActiveGuides() {
     const activeGuides = [];
-    activeEditor = vscode.window.activeTextEditor;
+    activeEditor = mustGetActiveTextEditor();
     if (activeGuidesTypes) {
         activeGuidesTypes.forEach((type) =>
             activeEditor.setDecorations(type, [])
@@ -548,7 +549,7 @@ function decorateActiveGuides() {
     }
     activeEditor.selections.forEach((selection) => {
         const doc = activeEditor.document;
-        const mirrorDoc = docMirror.getDocument(doc);
+        const mirrorDoc = docMirror.mustGetDocument(doc);
         const cursor = mirrorDoc.getTokenCursor(doc.offsetAt(selection.start));
         const visitedEndPositions = [selection.start];
         findActiveGuide: while (cursor.forwardList() && cursor.upList()) {
@@ -585,7 +586,7 @@ function decorateActiveGuides() {
 }
 
 export function activate(context: vscode.ExtensionContext) {
-    activeEditor = vscode.window.activeTextEditor;
+    activeEditor = mustGetActiveTextEditor();
 
     vscode.window.onDidChangeActiveTextEditor(
         (editor) => {
@@ -601,7 +602,7 @@ export function activate(context: vscode.ExtensionContext) {
     vscode.window.onDidChangeTextEditorSelection(
         (event) => {
             if (
-                event.textEditor === vscode.window.activeTextEditor &&
+                event.textEditor === getActiveTextEditor() &&
                 is_clojure(event.textEditor)
             ) {
                 if (lastHighlightedEditor !== event.textEditor) {
diff --git a/src/lsp/main.ts b/src/lsp/main.ts
index 73486d471..09ba061f5 100644
--- a/src/lsp/main.ts
+++ b/src/lsp/main.ts
@@ -299,7 +299,7 @@ function registerLspCommand(
         (m) => m.substring(1).toUpperCase()
     )}`;
     return vscode.commands.registerCommand(vscodeCommand, async () => {
-        const editor = vscode.window.activeTextEditor;
+        const editor = util.mustGetActiveTextEditor();
         const document = util.getDocument(editor.document);
         if (document && document.languageId === 'clojure') {
             const line = editor.selection.start.line;
@@ -320,7 +320,7 @@ function registerLspCommand(
 }
 
 async function codeLensReferencesHandler(_, line, character): Promise<void> {
-    vscode.window.activeTextEditor.selection = new vscode.Selection(
+    util.mustGetActiveTextEditor().selection = new vscode.Selection(
         line - 1,
         character - 1,
         line - 1,
@@ -332,12 +332,8 @@ async function codeLensReferencesHandler(_, line, character): Promise<void> {
 }
 
 function resolveMacroAsCommandHandler(): void {
-    const activeTextEditor = vscode.window.activeTextEditor;
-    if (
-        activeTextEditor &&
-        activeTextEditor.document &&
-        activeTextEditor.document.languageId === 'clojure'
-    ) {
+    const activeTextEditor = util.getActiveTextEditor();
+    if (activeTextEditor?.document?.languageId === 'clojure') {
         const documentUri = decodeURIComponent(
             activeTextEditor.document.uri.toString()
         );
diff --git a/src/namespace.ts b/src/namespace.ts
index 11d97728e..121c53a4d 100644
--- a/src/namespace.ts
+++ b/src/namespace.ts
@@ -16,7 +16,7 @@ export function getNamespace(doc: vscode.TextDocument) {
     if (doc && doc.languageId == 'clojure') {
         try {
             const cursor: LispTokenCursor = docMirror
-                .getDocument(doc)
+                .mustGetDocument(doc)
                 .getTokenCursor(0);
             cursor.forwardWhitespace(true);
             let token: Token = null,
diff --git a/src/paredit/extension.ts b/src/paredit/extension.ts
index a037d994b..2c7ec9def 100644
--- a/src/paredit/extension.ts
+++ b/src/paredit/extension.ts
@@ -365,7 +365,7 @@ function wrapPareditCommand(command: PareditCommand) {
     return () => {
         try {
             const textEditor = window.activeTextEditor,
-                mDoc: EditableDocument = docMirror.getDocument(
+                mDoc: EditableDocument = docMirror.mustGetDocument(
                     textEditor.document
                 );
             if (!enabled || !languages.has(textEditor.document.languageId)) {
diff --git a/src/providers/annotations.ts b/src/providers/annotations.ts
index f999fb2be..7b6eda148 100644
--- a/src/providers/annotations.ts
+++ b/src/providers/annotations.ts
@@ -95,7 +95,7 @@ function setSelectionDecorations(editor, ranges, status) {
 }
 
 function clearEvaluationDecorations(editor?: vscode.TextEditor) {
-    editor = editor || vscode.window.activeTextEditor;
+    editor = editor || util.getActiveTextEditor();
     if (editor) {
         util.cljsLib.removeStateValue(
             editor.document.uri + ':resultDecorationRanges'
@@ -204,8 +204,7 @@ function decorateSelection(
 
 function onDidChangeTextDocument(event: vscode.TextDocumentChangeEvent) {
     if (event.contentChanges.length) {
-        const activeTextEditor: vscode.TextEditor =
-            vscode.window.activeTextEditor;
+        const activeTextEditor: vscode.TextEditor = util.getActiveTextEditor();
         if (activeTextEditor) {
             const activeDocument = activeTextEditor.document,
                 changeDocument = event.document;
diff --git a/src/providers/completion.ts b/src/providers/completion.ts
index 4296f151b..896d3c584 100644
--- a/src/providers/completion.ts
+++ b/src/providers/completion.ts
@@ -49,7 +49,7 @@ export async function provideCompletionItems(
             toplevel = document.getText(toplevelSelection),
             toplevelStartOffset = document.offsetAt(toplevelSelection.start),
             toplevelStartCursor = docMirror
-                .getDocument(document)
+                .mustGetDocument(document)
                 .getTokenCursor(toplevelStartOffset + 1),
             wordRange = document.getWordRangeAtPosition(position),
             wordStartLocalOffset =
diff --git a/src/providers/hover.ts b/src/providers/hover.ts
index 45c324cbe..d4ab94955 100644
--- a/src/providers/hover.ts
+++ b/src/providers/hover.ts
@@ -34,7 +34,7 @@ export async function provideHover(
 
                 hovers.push(docsMd, clojureDocsMd);
             }
-            const editor = vscode.window.activeTextEditor;
+            const editor = util.mustGetActiveTextEditor();
 
             const context = {
                 ns,
diff --git a/src/providers/signature.ts b/src/providers/signature.ts
index b868a36fd..22ee10ffc 100644
--- a/src/providers/signature.ts
+++ b/src/providers/signature.ts
@@ -75,7 +75,7 @@ export async function provideSignatureHelp(
 
 function getCurrentArgsRanges(document: TextDocument, idx: number): Range[] {
     const cursor: LispTokenCursor = docMirror
-            .getDocument(document)
+            .mustGetDocument(document)
             .getTokenCursor(idx),
         allRanges = cursor.rowColRangesForSexpsInList('(');
 
@@ -112,7 +112,7 @@ function getActiveSignatureIdx(
 
 function getSymbol(document: TextDocument, idx: number): string {
     const cursor: LispTokenCursor = docMirror
-        .getDocument(document)
+        .mustGetDocument(document)
         .getTokenCursor(idx);
     return cursor.getFunctionName();
 }
@@ -123,7 +123,7 @@ function coordsToRange(coords: [[number, number], [number, number]]): Range {
 
 function getPreviousRangeIndexAndFunction(document: TextDocument, idx: number) {
     const peekBehindCursor: LispTokenCursor = docMirror
-        .getDocument(document)
+        .mustGetDocument(document)
         .getTokenCursor(idx);
     peekBehindCursor.backwardFunction(1);
     const previousFunction = peekBehindCursor.getFunctionName(0),
diff --git a/src/results-output/repl-history.ts b/src/results-output/repl-history.ts
index a154de79c..c91962ca5 100644
--- a/src/results-output/repl-history.ts
+++ b/src/results-output/repl-history.ts
@@ -117,7 +117,7 @@ function prependNewline(text: string) {
 }
 
 function showPreviousReplHistoryEntry(): void {
-    const editor = vscode.window.activeTextEditor;
+    const editor = util.mustGetActiveTextEditor();
     const doc = editor.document;
     const replSessionType = getSessionType();
     const history = getHistory(replSessionType);
@@ -139,7 +139,7 @@ function showPreviousReplHistoryEntry(): void {
 }
 
 function showNextReplHistoryEntry(): void {
-    const editor = vscode.window.activeTextEditor;
+    const editor = util.mustGetActiveTextEditor();
     const doc = editor.document;
     const replSessionType = getSessionType();
     const history = getHistory(replSessionType);
diff --git a/src/results-output/results-doc.ts b/src/results-output/results-doc.ts
index 25d1bf4ca..18e850b3c 100644
--- a/src/results-output/results-doc.ts
+++ b/src/results-output/results-doc.ts
@@ -186,7 +186,7 @@ export async function initResultsDoc(): Promise<vscode.TextDocument> {
                 const document = event.textEditor.document;
                 if (isResultsDoc(document)) {
                     const idx = document.offsetAt(event.selections[0].active);
-                    const mirrorDoc = docMirror.getDocument(document);
+                    const mirrorDoc = docMirror.mustGetDocument(document);
                     const selectionCursor = mirrorDoc.getTokenCursor(idx);
                     selectionCursor.forwardWhitespace();
                     if (selectionCursor.atEnd()) {
@@ -219,14 +219,10 @@ export async function initResultsDoc(): Promise<vscode.TextDocument> {
 
     // If the output window is active when initResultsDoc is run, these contexts won't be set properly without the below
     // until the next time it's focused
-    if (
-        vscode.window.activeTextEditor &&
-        isResultsDoc(vscode.window.activeTextEditor.document)
-    ) {
+    const activeTextEditor = util.getActiveTextEditor();
+    if (activeTextEditor && isResultsDoc(activeTextEditor.document)) {
         setContextForOutputWindowActive(true);
-        replHistory.setReplHistoryCommandsActiveContext(
-            vscode.window.activeTextEditor
-        );
+        replHistory.setReplHistoryCommandsActiveContext(activeTextEditor);
     }
     replHistory.resetState();
     isInitialized = true;
@@ -270,7 +266,7 @@ export async function setNamespaceFromCurrentFile() {
 async function appendFormGrabbingSessionAndNS(topLevel: boolean) {
     const session = replSession.getSession();
     const ns = namespace.getNamespace(util.getDocument({}));
-    const editor = vscode.window.activeTextEditor;
+    const editor = util.mustGetActiveTextEditor();
     const doc = editor.document;
     const selection = editor.selection;
     let code = '';
diff --git a/src/select.ts b/src/select.ts
index 6242392f4..82f456358 100644
--- a/src/select.ts
+++ b/src/select.ts
@@ -18,7 +18,7 @@ function getFormSelection(
     topLevel: boolean
 ): vscode.Selection {
     const idx = doc.offsetAt(pos);
-    const cursor = docMirror.getDocument(doc).getTokenCursor(idx);
+    const cursor = docMirror.mustGetDocument(doc).getTokenCursor(idx);
     const range = topLevel
         ? cursor.rangeForDefun(idx)
         : cursor.rangeForCurrentForm(idx);
@@ -32,7 +32,7 @@ function getEnclosingFormSelection(
     pos: vscode.Position
 ): vscode.Selection {
     const idx = doc.offsetAt(pos);
-    const cursor = docMirror.getDocument(doc).getTokenCursor(idx);
+    const cursor = docMirror.mustGetDocument(doc).getTokenCursor(idx);
     if (cursor.backwardList()) {
         cursor.backwardUpList();
         const start = cursor.offsetStart;
@@ -52,7 +52,7 @@ function selectForm(
     ) => vscode.Selection,
     toplevel: boolean
 ) {
-    const editor = vscode.window.activeTextEditor,
+    const editor = util.mustGetActiveTextEditor(),
         doc = util.getDocument(document),
         selection = editor.selection;
 
diff --git a/src/testRunner.ts b/src/testRunner.ts
index 68c371ec1..702727b3e 100644
--- a/src/testRunner.ts
+++ b/src/testRunner.ts
@@ -359,7 +359,7 @@ async function runNamespaceTests(
 }
 
 function getTestUnderCursor() {
-    const editor = vscode.window.activeTextEditor;
+    const editor = util.getActiveTextEditor();
     if (editor) {
         return getText.currentTopLevelFunction(editor?.document)[1];
     }
@@ -406,7 +406,7 @@ function runNamespaceTestsCommand(controller: vscode.TestController) {
     }
     runNamespaceTests(
         controller,
-        vscode.window.activeTextEditor.document
+        util.mustGetActiveTextEditor().document
     ).catch((msg) => {
         void vscode.window.showWarningMessage(msg);
     });
@@ -474,7 +474,7 @@ function initialize(controller: vscode.TestController): void {
             // The next steps here would be to turn request.exclude and requst.include
             // into a Cider var-query that can be passed to test-var query directly.
             const namespaces = util.distinct(runItems.map((ri) => ri[0]));
-            const doc = vscode.window.activeTextEditor.document;
+            const doc = util.mustGetActiveTextEditor().document;
             runNamespaceTestsImpl(controller, doc, namespaces).catch((msg) => {
                 void vscode.window.showWarningMessage(msg);
             });
diff --git a/src/util/get-text.ts b/src/util/get-text.ts
index f540f2916..3d19f93f3 100644
--- a/src/util/get-text.ts
+++ b/src/util/get-text.ts
@@ -46,7 +46,7 @@ export function currentEnclosingFormText(
 
 export function currentFunction(doc: vscode.TextDocument): SelectionAndText {
     if (doc) {
-        const tokenCursor = docMirror.getDocument(doc).getTokenCursor();
+        const tokenCursor = docMirror.mustGetDocument(doc).getTokenCursor();
         const [start, end] = tokenCursor.getFunctionSexpRange();
         if (start && end) {
             const startPos = doc.positionAt(start);
@@ -63,7 +63,7 @@ function selectionAndText(
     textGetter: (doc: EditableDocument) => cursorTextGetter.RangeAndText
 ): SelectionAndText {
     if (doc) {
-        const mirrorDoc = docMirror.getDocument(doc);
+        const mirrorDoc = docMirror.mustGetDocument(doc);
         const [range, text] = textGetter(mirrorDoc);
         if (range) {
             return [select.selectionFromOffsetRange(doc, range), text];
@@ -99,7 +99,7 @@ function fromFn(
     cursorDocFn: (doc: EditableDocument, offset?: number) => [number, number]
 ): SelectionAndText {
     if (doc) {
-        const cursorDoc = docMirror.getDocument(doc);
+        const cursorDoc = docMirror.mustGetDocument(doc);
         const range = cursorDocFn(cursorDoc);
         const selection = select.selectionFromOffsetRange(doc, range);
         const text = doc.getText(selection);
diff --git a/src/utilities.ts b/src/utilities.ts
index f3b04f023..49f0dec0f 100644
--- a/src/utilities.ts
+++ b/src/utilities.ts
@@ -9,6 +9,7 @@ import * as JSZip from 'jszip';
 import * as outputWindow from './results-output/results-doc';
 import * as cljsLib from '../out/cljs-lib/cljs-lib';
 import * as url from 'url';
+import { isUndefined } from 'lodash';
 
 const specialWords = ['-', '+', '/', '*']; //TODO: Add more here
 const syntaxQuoteSymbol = '`';
@@ -174,17 +175,17 @@ function getWordAtPosition(document, position) {
 function getDocument(
     document: vscode.TextDocument | Record<string, never>
 ): vscode.TextDocument {
+    const activeTextEditor = getActiveTextEditor();
     if (
         document &&
         Object.prototype.hasOwnProperty.call(document, 'fileName')
     ) {
         return document as vscode.TextDocument;
     } else if (
-        vscode.window.activeTextEditor &&
-        vscode.window.activeTextEditor.document &&
-        vscode.window.activeTextEditor.document.languageId !== 'Log'
+        activeTextEditor?.document &&
+        activeTextEditor.document.languageId !== 'Log'
     ) {
-        return vscode.window.activeTextEditor.document;
+        return activeTextEditor.document;
     } else if (vscode.window.visibleTextEditors.length > 0) {
         const editor = vscode.window.visibleTextEditors.find(
             (editor) => editor.document && editor.document.languageId !== 'Log'
@@ -297,7 +298,7 @@ function markError(error) {
     }
 
     const diagnostic = cljsLib.getStateValue('diagnosticCollection'),
-        editor = vscode.window.activeTextEditor;
+        editor = mustGetActiveTextEditor();
 
     //editor.selection = new vscode.Selection(position, position);
     const line = error.line - 1,
@@ -346,7 +347,7 @@ function markWarning(warning) {
     }
 
     const diagnostic = cljsLib.getStateValue('diagnosticCollection'),
-        editor = vscode.window.activeTextEditor;
+        editor = mustGetActiveTextEditor();
 
     //editor.selection = new vscode.Selection(position, position);
     const line = Math.max(0, warning.line - 1),
@@ -556,6 +557,20 @@ function distinct<T>(coll: T[]): T[] {
     return [...new Set(coll)];
 }
 
+function getActiveTextEditor(): vscode.TextEditor | undefined {
+    return vscode.window.activeTextEditor;
+}
+
+function mustGetActiveTextEditor(): vscode.TextEditor {
+    const editor = getActiveTextEditor();
+
+    if (isUndefined(editor)) {
+        throw new Error('Expected active text editor!');
+    }
+
+    return editor;
+}
+
 export {
     distinct,
     getWordAtPosition,
@@ -592,4 +607,6 @@ export {
     cljsLib,
     randomSlug,
     isWindows,
+    getActiveTextEditor,
+    mustGetActiveTextEditor,
 };
diff --git a/src/when-contexts.ts b/src/when-contexts.ts
index 51fedd69c..6fbe8a671 100644
--- a/src/when-contexts.ts
+++ b/src/when-contexts.ts
@@ -2,6 +2,7 @@ import * as vscode from 'vscode';
 import { deepEqual } from './util/object';
 import * as docMirror from './doc-mirror';
 import * as context from './cursor-doc/cursor-context';
+import * as util from './utilities';
 
 let lastContexts: context.CursorContext[] = [];
 
@@ -10,7 +11,7 @@ export default function setCursorContextIfChanged(editor: vscode.TextEditor) {
         !editor ||
         !editor.document ||
         editor.document.languageId !== 'clojure' ||
-        editor !== vscode.window.activeTextEditor
+        editor !== util.getActiveTextEditor()
     ) {
         return;
     }
@@ -27,7 +28,7 @@ function determineCursorContexts(
     document: vscode.TextDocument,
     position: vscode.Position
 ): context.CursorContext[] {
-    const mirrorDoc = docMirror.getDocument(document);
+    const mirrorDoc = docMirror.mustGetDocument(document);
     return context.determineContexts(mirrorDoc, document.offsetAt(position));
 }