Partial Function XCode 9 Issue

Question

So I have the following partial function implementation:

func addObserver(with notificationType: String) -> (@escaping (Notification) -> (Void)) -> NSObjectProtocol
{
    return { (function: @escaping  (Notification) -> (Void)) in
    NotificationCenter.default.addObserver(forName: NSNotification.Name(rawValue: notificationType), object: nil, queue: nil, using: function)
    }
}

Which basically would be used as such to create a full function such as:

let aoSelectCountry = addObserver(with: selectCountryNotification)

Which would then be used as:

self.selectCountryObserver = aoSelectCountry{ (notification) in
            if (notification.object != nil) {
                //do things
            }
        }

This is effectively the same as writing:

self.selectCountryObserver = NotificationCenter.default.addObserver(forName: NSNotification.Name(rawValue: selectCountryNotification), object: nil, queue: nil) { (notification) in
            if (notification.object != nil) {
                //do things
            }

Now all of this worked in XCode 8. But when I try to compile in XCode 9, I get the following error:

Cannot convert value of type '(Notification) -> (Void)' to expected argument type '(Notification) -> Void'

Removing the brackets around the (Void) part of the initial function just changes the error message to:

Cannot convert value of type '(Notification) -> Void' to expected argument type '(Notification) -> Void'

I have a strong feeling that this is a compiler bug, but I do desperately need a work around. I appreciate anyone's efforts. Thanks!