Allow Animated.parallel to accept empty element in the array

Libraries/Animation/Animated/Animated.js

@@ -1177,7 +1177,7 @@ var parallel = function(
       }
 
       animations.forEach((animation, idx) => {
-        animation.start(endResult => {
+        var cb = function(endResult) {
           hasEnded[idx] = true;
           doneCount++;
           if (doneCount === animations.length) {
@@ -1189,7 +1189,13 @@ var parallel = function(
           if (!endResult.finished && stopTogether) {
             result.stop();
           }
-        });
+        };
+
+        if (!animation) {
+          cb({finished: true});
+        } else {
+          animation.start(cb);
+        }
       });
     },
 

Libraries/Animation/Animated/__tests__/Animated-test.js

@@ -205,6 +205,16 @@ describe('Animated Parallel', () => {
     expect(cb).toBeCalledWith({finished: true});
   });
 
+  it('works with an empty element in array', () => {
+    var anim1 = {start: jest.genMockFunction()};
+    var cb = jest.genMockFunction();
+    Animated.parallel([null, anim1]).start(cb);
+
+    expect(anim1.start).toBeCalled();
+    anim1.start.mock.calls[0][0]({finished: true});
+
+    expect(cb).toBeCalledWith({finished: true});
+  });
 
   it('parellelizes well', () => {
     var anim1 = {start: jest.genMockFunction()};