Swift and Xcode Thread 1: signal SIGABRT error on YPDrawSignatureView - digital-signature

Question

I try to use the YPDrawSignatureView for make an eSignature to my Swift 3.3 project with Xcode 9.3 version.
First I pulled the YPDrawSignatureView.swift to my project.
After I made two buttons and an UIImage to Main.storyboard. These objects pulled to my ViewController.swift and finally I have written my sample code in ViewController.swift:
import UIKit
class ViewController: UIViewController, YPSignatureDelegate {
#IBOutlet weak var signatureView: YPDrawSignatureView!
// Function for clearing the content of signature view
#IBAction func clearSignature(_ sender: UIButton) {
// This is how the signature gets cleared
self.signatureView.clear()
}
// Function for saving signature
#IBAction func saveSignature(_ sender: UIButton) {
// Getting the Signature Image from self.drawSignatureView using the method getSignature().
if let signatureImage = self.signatureView.getSignature(scale: 10) {
// Saving signatureImage from the line above to the Photo Roll.
// The first time you do this, the app asks for access to your pictures.
UIImageWriteToSavedPhotosAlbum(signatureImage, nil, nil, nil)
// Since the Signature is now saved to the Photo Roll, the View can be cleared anyway.
self.signatureView.clear()
}
}
// didStart() is called right after the first touch is registered in the view.
// For example, this can be used if the view is embedded in a scroll view, temporary
// stopping it from scrolling while signing.
func didStart() {
print("Started Drawing")
}
// didFinish() is called rigth after the last touch of a gesture is registered in the view.
// Can be used to enabe scrolling in a scroll view if it has previous been disabled.
func didFinish() {
print("Finished Drawing")
}
override func viewDidLoad() {
super.viewDidLoad()
signatureView.delegate = self
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
}
And when I tried to run my app, I got an error message from Xcode:
And here is the output window:
2018-04-04 10:57:17.936377+0200 Alairas3[413:70689] * Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[ setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key clearSignature.'
* First throw call stack:
(0x183496d8c 0x1826505ec 0x1834969f0 0x183dec44c 0x18d5085d4 0x18d94ba08 0x1833a4b24 0x18d6d90e4 0x18d50aadc 0x18d14e0f0 0x18d072b90 0x18d072acc 0x18d063d60 0x18d062b94 0x18d0f06a8 0x18d0662f0 0x18d03365c 0x18d663a0c 0x18d032e4c 0x18d032ce8 0x18d031b78 0x18dcc772c 0x18d031268 0x18daac9b8 0x18dbfaae8 0x18d030c88 0x18d030624 0x18d02d65c 0x18d02d3ac 0x185c94470 0x185c9cd6c 0x101735220 0x101741850 0x185cc8878 0x185cc851c 0x185cc8ab8 0x18343f404 0x18343ec2c 0x18343c79c 0x18335cda8 0x18533f020 0x18d33d78c 0x1009b0ae4 0x182dedfc0)
libc++abi.dylib: terminating with uncaught exception of type NSException
Please, help me, what is wrong?