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

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

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