     
     :returns: The created NSLayoutConstraint for this bottom attribute relation
     */
-    func addBottomConstraint(toView view: UIView, attribute: NSLayoutAttribute, relation: NSLayoutRelation, constant: CGFloat) -> NSLayoutConstraint {
+    func addBottomConstraint(toView view: UIView?, attribute: NSLayoutAttribute, relation: NSLayoutRelation, constant: CGFloat) -> NSLayoutConstraint {
         
         let constraint: NSLayoutConstraint = self.createConstraint(attribute: .Bottom, toView: view, attribute: attribute, relation: relation, constant: constant)
         self.superview?.addConstraint(constraint)

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