refactor(EventEmitter): optional emits (angular#10058)

the Subject#next is optional

Author: PatrickJS

modules/@angular/facade/src/async.ts

@@ -130,7 +130,7 @@ export class EventEmitter<T> extends Subject<T> {
     this.__isAsync = isAsync;
   }
 
-  emit(value: T) { super.next(value); }
+  emit(value?: T) { super.next(value); }
 
   /**
    * @deprecated - use .emit(value) instead

tools/public_api_guard/core/index.d.ts

@@ -715,7 +715,7 @@ export declare function enableProdMode(): void;
 export declare class EventEmitter<T> extends Subject<T> {
     __isAsync: boolean;
     constructor(isAsync?: boolean);
-    emit(value: T): void;
+    emit(value?: T): void;
     /** @deprecated */ next(value: any): void;
     subscribe(generatorOrNext?: any, error?: any, complete?: any): any;
 }