Unable to call more than once.

Hi, I have gotten this error while attempting to receive calls more than twice.

`Attempting to invoke virtual method 'com.quickbox.videochat.webrtc.view.QBRTCVideoTrack com.quickblox.videochat.webrtc.QBMediaStreamManager.getVideotrack(java.lang.Integer)' on a null object reference`

Is there any steps I am missing out to end call properly and ensure that this doesnt happen?

Thanks!