             
             override func callback(change: [String : AnyObject]) {
                 if let old = change[NSKeyValueChangeOldKey] {
-                    self.sink.put(old)
+                    self.put(old)
                 }
             }
         }

            }
            
            override func callback(change: [String : AnyObject]) {
                self.sink.put(change)
            }
        }
        

            
            override func callback(change: [String : AnyObject]) {
                if let old = change[NSKeyValueChangeOldKey], new = change[NSKeyValueChangeNewKey] {
                    self.put(old: old, new: new)
                }
            }
        }
