Custom UIButton class swift

I was curious of how to create a custom class for a UI element (say for example, a button)?

I've read the Apple development docs and I followed the instructions, what I thought was to create a separate UIButton class file and link that class file for all buttons on the storyboard.

Here's the separate UIButton class code (file named buttonz.swift):

import UIKit

public class buttonz: UIButton {


    required public init?(coder aDecoder: NSCoder) {

        super.init(coder: aDecoder)

        self.layer.borderWidth = 1
        self.backgroundColor = UIColor.whiteColor()
        self.layer.borderColor = UIColor.blackColor().CGColor

    }

}

And on the storyboard, I linked that specific button to the new UIButton class:

The problem is that when I run the simulator, it gives me an error in the debig console:

this class is not key value coding-compliant for the key aButton

I thought the process was straightforward in the guide but am I missing any extra steps? Please let me know, thanks!

For reference, here is the link to the Apple docs that I used as a guide.

https://developer.apple.com/library/ios/referencelibrary/GettingStarted/DevelopiOSAppsSwift/Lesson5.html

Edit 1 - Here's the action link to the viewcontroller.swift for the view controller. I just ctrl + dragged the button from the story board into the viewcontroller.swift.

 @IBAction func a(sender: AnyObject) {
        var alertView = UIAlertView();
        alertView.addButtonWithTitle("Ok");
        alertView.title = "title";
        alertView.message = "message";
        alertView.show();
    }