diff --git a/src/vs/editor/browser/editorExtensions.ts b/src/vs/editor/browser/editorExtensions.ts
index e7494cc7a976a444d8850eedfa4d4fee41a872ee..c467768414b1bf09dbb9bef5c3620462e2991961 100644
--- a/src/vs/editor/browser/editorExtensions.ts
+++ b/src/vs/editor/browser/editorExtensions.ts
@@ -241,7 +241,7 @@ export abstract class EditorAction extends EditorCommand {
 
 // --- Registration of commands and actions
 
-export function registerLanguageCommand(id: string, handler: (accessor: ServicesAccessor, args: { [n: string]: any }) => any) {
+export function registerLanguageCommand<Args extends { [n: string]: any }>(id: string, handler: (accessor: ServicesAccessor, args: Args) => any) {
 	CommandsRegistry.registerCommand(id, (accessor, args) => handler(accessor, args || {}));
 }
 
diff --git a/src/vs/platform/instantiation/common/instantiation.ts b/src/vs/platform/instantiation/common/instantiation.ts
index 735c035934cca1726130affcd2a12bec68b5ad41..ef35c1f030a8b9686a8982817e2d4c81a6271afb 100644
--- a/src/vs/platform/instantiation/common/instantiation.ts
+++ b/src/vs/platform/instantiation/common/instantiation.ts
@@ -22,40 +22,42 @@ export namespace _util {
 
 // --- interfaces ------
 
+type BrandedService = { _serviceBrand: undefined };
+
 export interface IConstructorSignature0<T> {
-	new(...services: { _serviceBrand: undefined; }[]): T;
+	new(...services: BrandedService[]): T;
 }
 
 export interface IConstructorSignature1<A1, T> {
-	new(first: A1, ...services: { _serviceBrand: undefined; }[]): T;
+	new(first: A1, ...services: BrandedService[]): T;
 }
 
 export interface IConstructorSignature2<A1, A2, T> {
-	new(first: A1, second: A2, ...services: { _serviceBrand: undefined; }[]): T;
+	new(first: A1, second: A2, ...services: BrandedService[]): T;
 }
 
 export interface IConstructorSignature3<A1, A2, A3, T> {
-	new(first: A1, second: A2, third: A3, ...services: { _serviceBrand: undefined; }[]): T;
+	new(first: A1, second: A2, third: A3, ...services: BrandedService[]): T;
 }
 
 export interface IConstructorSignature4<A1, A2, A3, A4, T> {
-	new(first: A1, second: A2, third: A3, fourth: A4, ...services: { _serviceBrand: undefined; }[]): T;
+	new(first: A1, second: A2, third: A3, fourth: A4, ...services: BrandedService[]): T;
 }
 
 export interface IConstructorSignature5<A1, A2, A3, A4, A5, T> {
-	new(first: A1, second: A2, third: A3, fourth: A4, fifth: A5, ...services: { _serviceBrand: undefined; }[]): T;
+	new(first: A1, second: A2, third: A3, fourth: A4, fifth: A5, ...services: BrandedService[]): T;
 }
 
 export interface IConstructorSignature6<A1, A2, A3, A4, A5, A6, T> {
-	new(first: A1, second: A2, third: A3, fourth: A4, fifth: A5, sixth: A6, ...services: { _serviceBrand: undefined; }[]): T;
+	new(first: A1, second: A2, third: A3, fourth: A4, fifth: A5, sixth: A6, ...services: BrandedService[]): T;
 }
 
 export interface IConstructorSignature7<A1, A2, A3, A4, A5, A6, A7, T> {
-	new(first: A1, second: A2, third: A3, fourth: A4, fifth: A5, sixth: A6, seventh: A7, ...services: { _serviceBrand: undefined; }[]): T;
+	new(first: A1, second: A2, third: A3, fourth: A4, fifth: A5, sixth: A6, seventh: A7, ...services: BrandedService[]): T;
 }
 
 export interface IConstructorSignature8<A1, A2, A3, A4, A5, A6, A7, A8, T> {
-	new(first: A1, second: A2, third: A3, fourth: A4, fifth: A5, sixth: A6, seventh: A7, eigth: A8, ...services: { _serviceBrand: undefined; }[]): T;
+	new(first: A1, second: A2, third: A3, fourth: A4, fifth: A5, sixth: A6, seventh: A7, eigth: A8, ...services: BrandedService[]): T;
 }
 
 export interface ServicesAccessor {
diff --git a/src/vs/workbench/contrib/files/browser/views/openEditorsView.ts b/src/vs/workbench/contrib/files/browser/views/openEditorsView.ts
index f25cd1c755488094506e3e497cb3d985cba93cab..95aa5d90a6e78da2fdb76a160e07ce3fffb65502 100644
--- a/src/vs/workbench/contrib/files/browser/views/openEditorsView.ts
+++ b/src/vs/workbench/contrib/files/browser/views/openEditorsView.ts
@@ -244,8 +244,9 @@ export class OpenEditorsView extends ViewletPanel {
 			this.dirtyEditorFocusedContext.reset();
 			const element = e.elements.length ? e.elements[0] : undefined;
 			if (element instanceof OpenEditor) {
-				this.dirtyEditorFocusedContext.set(this.textFileService.isDirty(withNullAsUndefined(element.getResource())));
-				this.resourceContext.set(withUndefinedAsNull(element.getResource()));
+				const resource = element.getResource();
+				this.dirtyEditorFocusedContext.set(this.textFileService.isDirty(resource));
+				this.resourceContext.set(withUndefinedAsNull(resource));
 			} else if (!!element) {
 				this.groupFocusedContext.set(true);
 			}
diff --git a/src/vs/workbench/services/textfile/common/textFileEditorModel.ts b/src/vs/workbench/services/textfile/common/textFileEditorModel.ts
index bd6332610d8058c1b846a3b56940c45c0552f910..3181a91d1c1c08fa70b240be497b1c586d8917d3 100644
--- a/src/vs/workbench/services/textfile/common/textFileEditorModel.ts
+++ b/src/vs/workbench/services/textfile/common/textFileEditorModel.ts
@@ -80,7 +80,7 @@ export class TextFileEditorModel extends BaseTextEditorModel implements ITextFil
 	private contentEncoding: string; 	// encoding as reported from disk
 	private preferredEncoding: string;	// encoding as chosen by the user
 
-	private preferredMode: string;		// mode as chosen by the user
+	private preferredMode: string | undefined;	// mode as chosen by the user
 
 	private versionId: number;
 	private bufferSavedVersionId: number;
@@ -108,7 +108,7 @@ export class TextFileEditorModel extends BaseTextEditorModel implements ITextFil
 	constructor(
 		resource: URI,
 		preferredEncoding: string,
-		preferredMode: string,
+		preferredMode: string | undefined,
 		@INotificationService private readonly notificationService: INotificationService,
 		@IModeService modeService: IModeService,
 		@IModelService modelService: IModelService,