     private weak var pipCallVC: CallViewController?
     private var uiOperationQueue: OperationQueue = .main
     private var isStarted: Bool = false
-    private var callTimer: Timer!
+    private var callTimer: Timer?
     
     private var isCallKitEnabled: Bool {
         MXCallKitAdapter.callKitAvailable() && MXKAppSettings.standard()?.isCallKitEnabled == true

            }
        case .connected:
            NSLog("[CallService] callStateChanged: call connected: \(call.callId)")
            callTimer.fire()
        case .onHold:
            NSLog("[CallService] callStateChanged: call holded: \(call.callId)")
            callTimer.fire()
            callHolded(withCallId: call.callId)
        case .remotelyOnHold:
            NSLog("[CallService] callStateChanged: call remotely holded: \(call.callId)")
            callTimer.fire()
            callHolded(withCallId: call.callId)
        case .ended:
            NSLog("[CallService] callStateChanged: call ended: \(call.callId)")

    }
    
    private func stopCallTimer() {
        callTimer?.invalidate()
        callTimer = nil
    }
    
