     private func triggerCallbacks(status: AKMIDIStatus,
                                   noteNumber: MIDINoteNumber,
                                   velocity: MIDIVelocity) {
-        for callback in callbacks {
-            callback(status, noteNumber, velocity)
+        if callback != nil {
+            callback!(status, noteNumber, velocity)
         }
     }
 

    // MARK: Properties

    /// All callbacks that will get triggered by MIDI events
    public var callbacks = [AKMIDICallback]()

    /// Initialize the callback instrument
    ///

        super.init()
        let midi = AKMIDI()
        self.enableMIDI(midi.client, name: "callback midi in")
        self.callback = callback
        avAudioNode = AVAudioMixerNode()
        AudioKit.engine.attachNode(self.avAudioNode)
    }
