diff --git a/src/vs/vscode.proposed.d.ts b/src/vs/vscode.proposed.d.ts
index 25669630ad3..9091b4edfdc 100644
--- a/src/vs/vscode.proposed.d.ts
+++ b/src/vs/vscode.proposed.d.ts
@@ -117,7 +117,7 @@ declare module 'vscode' {
 		/**
 		 * The rebuild all task group;
 		 */
-		public static RebuildAll: TaskGroup;
+		public static Rebuild: TaskGroup;
 
 		/**
 		 * The test all task group;
@@ -146,6 +146,11 @@ declare module 'vscode' {
 		 * ```
 		 */
 		readonly type: string;
+
+		/**
+		 * Additional attributes of a concrete task definition.
+		 */
+		[name: string]: any;
 	}
 
 	/**
@@ -298,7 +303,7 @@ declare module 'vscode' {
 		 * A human-readable string describing the source of this
 		 * shell task, e.g. 'gulp' or 'npm'.
 		 */
-		source?: string;
+		source: string;
 
 		/**
 		 * The task group this tasks belongs to. See TaskGroup
diff --git a/src/vs/workbench/api/node/extHostTypes.ts b/src/vs/workbench/api/node/extHostTypes.ts
index 8bd408c7e66..dd6938bdab3 100644
--- a/src/vs/workbench/api/node/extHostTypes.ts
+++ b/src/vs/workbench/api/node/extHostTypes.ts
@@ -1040,7 +1040,7 @@ export class TaskGroup implements vscode.TaskGroup {
 
 	public static Build: TaskGroup = new TaskGroup('build', 'Build');
 
-	public static RebuildAll: TaskGroup = new TaskGroup('rebuildAll', 'RebuildAll');
+	public static Rebuild: TaskGroup = new TaskGroup('rebuild', 'Rebuild');
 
 	public static Test: TaskGroup = new TaskGroup('clean', 'Clean');
 
@@ -1248,10 +1248,6 @@ export class Task implements vscode.Task {
 	}
 
 	set source(value: string) {
-		if (value === void 0 || value === null) {
-			this._source = undefined;
-			return;
-		}
 		if (typeof value !== 'string' || value.length === 0) {
 			throw illegalArgument('source must be a string of length > 0');
 		}
diff --git a/src/vs/workbench/parts/tasks/common/tasks.ts b/src/vs/workbench/parts/tasks/common/tasks.ts
index 3b7e2b8d6ff..43b7cd5a77b 100644
--- a/src/vs/workbench/parts/tasks/common/tasks.ts
+++ b/src/vs/workbench/parts/tasks/common/tasks.ts
@@ -203,16 +203,16 @@ export namespace TaskGroup {
 
 	export const Build: 'build' = 'build';
 
-	export const RebuildAll: 'rebuildAll' = 'rebuildAll';
+	export const Rebuild: 'rebuild' = 'rebuild';
 
 	export const Test: 'test' = 'test';
 
 	export function is(value: string): value is string {
-		return value === Clean || value === Build || value === RebuildAll || value === Test;
+		return value === Clean || value === Build || value === Rebuild || value === Test;
 	}
 }
 
-export type TaskGroup = 'clean' | 'build' | 'rebuildAll' | 'test';
+export type TaskGroup = 'clean' | 'build' | 'rebuild' | 'test';
 
 export enum TaskSourceKind {
 	Workspace = 1,