[UITextView becomeFirstResponder] crash with [__NSPlaceholderArray initWithObjects:count:]: attempt to insert nil object from objects[0]

I am trying to set my UITextView as the first responder with [self.textView becomeFirstResponder] when my view controller called viewDidAppear. But sometimes it will cause crash with the error: [__NSPlaceholderArray initWithObjects:count:]: attempt to insert nil object from objects[0]

all I did is just:

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    [self.textView becomeFirstResponder];
}

So if anyone can tell me what happened and how to do? when I call the [self.textView becomeFirstResponder], what will be insert into the responders list? self.textView itself?

Thanks very much!