strcit null checks

#60565

src/tsconfig.strictNullChecks.json

@@ -78,6 +78,7 @@
 		"./vs/base/common/winjs.base.d.ts",
 		"./vs/base/common/winjs.polyfill.promise.ts",
 		"./vs/base/common/worker/simpleWorker.ts",
+		"./vs/workbench/common/resources.ts",
 		"./vs/base/node/decoder.ts",
 		"./vs/base/node/id.ts",
 		"./vs/base/node/paths.ts",
@@ -313,4 +314,4 @@
 	"exclude": [
 		"./typings/require-monaco.d.ts"
 	]
-}
\ No newline at end of file
+}

src/vs/workbench/common/resources.ts

@@ -25,7 +25,7 @@ export class ResourceContextKey extends Disposable implements IContextKey<URI> {
 	private _resourceKey: IContextKey<URI>;
 	private _schemeKey: IContextKey<string>;
 	private _filenameKey: IContextKey<string>;
-	private _langIdKey: IContextKey<string>;
+	private _langIdKey: IContextKey<string | null>;
 	private _extensionKey: IContextKey<string>;
 	private _hasResource: IContextKey<boolean>;
 	private _isfileSystemResource: IContextKey<boolean>;
@@ -58,7 +58,7 @@ export class ResourceContextKey extends Disposable implements IContextKey<URI> {
 		this._resourceKey.set(value);
 		this._schemeKey.set(value && value.scheme);
 		this._filenameKey.set(value && paths.basename(value.fsPath));
-		this._langIdKey.set(value && this._modeService.getModeIdByFilepathOrFirstLine(value.fsPath));
+		this._langIdKey.set(value ? this._modeService.getModeIdByFilepathOrFirstLine(value.fsPath) : null);
 		this._extensionKey.set(value && paths.extname(value.fsPath));
 		this._hasResource.set(!!value);
 		this._isfileSystemResource.set(value && this._fileService.canHandleResource(value));