fix(Subscriber): do not call complete with undefined value param (#2559)

Author: kwonoj

spec/Subscriber-spec.ts

@@ -85,7 +85,7 @@ describe('Subscriber', () => {
   });
 
   it('should not be closed when other subscriber with same observer instance completes', () => {
-    let observer = {
+    const observer = {
       next: function () { /*noop*/ }
     };
 
@@ -97,4 +97,19 @@ describe('Subscriber', () => {
     expect(sub1.closed).to.be.false;
     expect(sub2.closed).to.be.true;
   });
+
+  it('should call complete observer without any arguments', () => {
+    let argument: Array<any> = null;
+
+    const observer = {
+      complete: (...args: Array<any>) => {
+        argument = args;
+      }
+    };
+
+    const sub1 = new Subscriber(observer);
+    sub1.complete();
+
+    expect(argument).to.have.lengthOf(0);
+  });
 });

src/Subscriber.ts

@@ -234,11 +234,13 @@ class SafeSubscriber<T> extends Subscriber<T> {
     if (!this.isStopped) {
       const { _parentSubscriber } = this;
       if (this._complete) {
+        const wrappedComplete = () => this._complete.call(this._context);
+
         if (!_parentSubscriber.syncErrorThrowable) {
-          this.__tryOrUnsub(this._complete);
+          this.__tryOrUnsub(wrappedComplete);
           this.unsubscribe();
         } else {
-          this.__tryOrSetError(_parentSubscriber, this._complete);
+          this.__tryOrSetError(_parentSubscriber, wrappedComplete);
           this.unsubscribe();
         }
       } else {