   /// Callback ID used to send a downloadFailure notification to JavaScript
   private var downloadFailureCallbackId: String?
 
-  private var startupTimer: METTimer!
+  private var startupTimer: METTimer?
 
   // MARK: - Lifecycle
 

  public func startupDidComplete(command: CDVInvokedUrlCommand) {
    NSLog("startupDidComplete")
    
    startupTimer.stop()
    
    lastKnownGoodVersion = currentAssetBundle.version


      currentAssetBundle = pendingAssetBundle
      self.pendingAssetBundle = nil
    }
    
    startupTimer?.startWithTimeInterval(startupTimeoutInterval)
  }
  
  // MARK: - Notifications
