Compile error in Swift 4 on parameter passing

I used 3rd party library in Xcode 9 Beta 3. And I am getting the following error in the completion call, I am not able to resolve this error:

DispatchQueue.main.asyncAfter(deadline: .now() + delay) { 
    self.animationView?.alpha = 0
    self.containerView.alpha  = 1
    completion?()    // -> Error: Missing argument parameter #1 in call.   
}

And getting the following warning in the completion function:

func openAnimation(_ completion: ((Void) -> Void)?) {    
    // -> Warning: When calling this function in Swift 4 or later, you must pass a '()' tuple; did you mean for the input type to be '()'?
}