AngularJS: make IDirective.link() arguments optional

angularjs/angular.d.ts

@@ -748,12 +748,14 @@ declare module ng {
             ) => any;
         controller?: any;
         controllerAs?: string;
+        // A link function with no arguments is perfectly valid; the norm seems
+        // to be passing the scope, element and attributes.
         link?:
-            (scope: IScope,
-            instanceElement: IAugmentedJQuery,
-            instanceAttributes: IAttributes,
-            controller: any,
-            transclude: ITranscludeFunction
+            (scope?: IScope,
+            instanceElement?: IAugmentedJQuery,
+            instanceAttributes?: IAttributes,
+            controller?: any,
+            transclude?: ITranscludeFunction
             ) => void;
         name?: string;
         priority?: number;