     
     :returns: The created NSLayoutConstraint for this center Y coordinate attribute relation
     */
-    func addCenterYConstraint(toView view: UIView, relation: NSLayoutRelation, constant: CGFloat) -> NSLayoutConstraint {
+    func addCenterYConstraint(toView view: UIView?, relation: NSLayoutRelation, constant: CGFloat) -> NSLayoutConstraint {
         
         let constraint: NSLayoutConstraint = self.createConstraint(attribute: .CenterY, toView: view, attribute: .CenterY, relation: relation, constant: constant)
         self.superview?.addConstraint(constraint)

    
    :returns: The created NSLayoutConstraint for this center Y coordinate attribute relation
    */
    func addCenterYConstraint(toView view: UIView, constant: CGFloat) -> NSLayoutConstraint {
        
        return self.addCenterYConstraint(toView: view, relation: .Equal, constant: constant)
    }

    
    :returns: The created NSLayoutConstraint for this top attribute relation
    */
    func addTopConstraint(toView view: UIView?, relation: NSLayoutRelation, constant: CGFloat) -> NSLayoutConstraint {
        
        return self.addTopConstraint(toView: view, attribute: .Top, relation: relation, constant: constant)
    }
