      - Returns: The bottom NSLayoutConstraint if found.
      */
     public var bottomConstraint: NSLayoutConstraint? {
-        return constraintForView(self, attribute: .bottom, existsOnView: self.superview)
+        return constraintForView(self, attribute: .bottom, existsOnView: superview)
     }
     
     /** Gets the height constraint if found.

    - Returns: The left NSLayoutConstraint if found.
     */
    public var leftConstraint: NSLayoutConstraint? {
        return constraintForView(self, attribute: .left, existsOnView: self.superview)
    }

    /** Gets the right constraint if found.

     - Returns: The trailing NSLayoutConstraint if found.
     */
    public var trailingConstraint: NSLayoutConstraint? {
        return constraintForView(self, attribute: .trailing, existsOnView: superview)
    }
    
    /** Gets the leading constraint if found.
