diff --git a/src/tsconfig.strictNullChecks.json b/src/tsconfig.strictNullChecks.json
index 6a2a529b032..6b1756b4778 100644
--- a/src/tsconfig.strictNullChecks.json
+++ b/src/tsconfig.strictNullChecks.json
@@ -142,6 +142,7 @@
 		"./vs/base/test/common/marshalling.test.ts",
 		"./vs/base/test/common/mime.test.ts",
 		"./vs/base/test/common/objects.test.ts",
+		"./vs/base/test/common/octicon.test.ts",
 		"./vs/base/test/common/paging.test.ts",
 		"./vs/base/test/common/paths.test.ts",
 		"./vs/base/test/common/resources.test.ts",
@@ -214,6 +215,7 @@
 		"./vs/editor/contrib/comment/comment.ts",
 		"./vs/editor/contrib/comment/lineCommentCommand.ts",
 		"./vs/editor/contrib/comment/test/blockCommentCommand.test.ts",
+		"./vs/editor/contrib/comment/test/lineCommentCommand.test.ts",
 		"./vs/editor/contrib/contextmenu/contextmenu.ts",
 		"./vs/editor/contrib/cursorUndo/cursorUndo.ts",
 		"./vs/editor/contrib/dnd/dnd.ts",
diff --git a/src/vs/base/test/common/octicon.test.ts b/src/vs/base/test/common/octicon.test.ts
index 9135c38e1e2..c91055525d2 100644
--- a/src/vs/base/test/common/octicon.test.ts
+++ b/src/vs/base/test/common/octicon.test.ts
@@ -8,7 +8,7 @@ import { matchesFuzzyOcticonAware, parseOcticons } from 'vs/base/common/octicon'
 
 export interface IOcticonFilter {
 	// Returns null if word doesn't match.
-	(query: string, target: { text: string, octiconOffsets?: number[] }): IMatch[];
+	(query: string, target: { text: string, octiconOffsets?: number[] }): IMatch[] | null;
 }
 
 function filterOk(filter: IOcticonFilter, word: string, target: { text: string, octiconOffsets?: number[] }, highlights?: { start: number; end: number; }[]) {
diff --git a/src/vs/editor/contrib/comment/test/lineCommentCommand.test.ts b/src/vs/editor/contrib/comment/test/lineCommentCommand.test.ts
index a32458d6abd..e9c0c51499a 100644
--- a/src/vs/editor/contrib/comment/test/lineCommentCommand.test.ts
+++ b/src/vs/editor/contrib/comment/test/lineCommentCommand.test.ts
@@ -950,7 +950,9 @@ suite('Editor Contrib - Line Comment in mixed modes', () => {
 
 			this._register(modes.TokenizationRegistry.register(this.getLanguageIdentifier().language, {
 				getInitialState: (): modes.IState => NULL_STATE,
-				tokenize: undefined,
+				tokenize: () => {
+					throw new Error('not implemented');
+				},
 				tokenize2: (line: string, state: modes.IState): TokenizationResult2 => {
 					let languageId = (/^  /.test(line) ? INNER_LANGUAGE_ID : OUTER_LANGUAGE_ID);