Animate cc error

Hi,

I am creating an animation for a touch screen with several sound sliders that control sound volume.

I is all working fine except I am getting this error for all the sliders I created

TypeError: Error #1009: Cannot access a property or method of a null object reference.

  at SinfoniasV13_3_2018530_fla::MainTimeline/onEnterFrame12()[SinfoniasV13_3_2018530_fla.MainTimeline::frame811:116]

[UnloadSWF] SinfoniasV13.3.2018530.swf

this is the code I used to control the volume:

var sliderValue:uint = (mypista1.botao1.x)/100;

var gain:caga = new caga(); 

var trans:SoundTransform;

trans = new SoundTransform(1, 0);

var channel:SoundChannel = gain.play(0, 100, trans);

channel.addEventListener(Event.SOUND_COMPLETE, onPlaybackComplete);

addEventListener(Event.ENTER_FRAME, onEnterFrame);

function onEnterFrame(event:Event):void

{

    trans.volume =mypista1.botao1.x *0.1;

    channel.soundTransform = trans; // or SoundMixer.soundTransform = trans;

}

function onPlaybackComplete(event:Event):void

{

    removeEventListener(Event.ENTER_FRAME, onEnterFrame);

}

This is the bit of code giving the error although  all working fine

{

    trans.volume =mypista1.botao1.x *0.1;

    channel.soundTransform = trans; // or SoundMixer.soundTransform = trans;

}

Thank you all in advance

Best

Ana