title: Fail to Upgrade to Android 8.1
body: <p>i have an existing project would i like upgrading from Android 8.0 to 8.1, but it failed. I reading the changes on Android 8.1, but i dont know what is exactly the problem. I have some failure in my logcat which you can see here: </p>
  
  <pre><code>    --------- beginning of crash
  04-12 08:57:55.605 3530-3530/? E/AndroidRuntime: FATAL EXCEPTION: main
      Process: com.example.teleoperation, PID: 3530
      android.app.RemoteServiceException: Bad notification for startForeground: java.lang.RuntimeException: invalid channel for service notification: Notification(channel=null pri=0 contentView=null vibrate=null sound=null tick defaults=0x0 flags=0x50 color=0x00000000 vis=PRIVATE)
          at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1768)
          at android.os.Handler.dispatchMessage(Handler.java:106)
          at android.os.Looper.loop(Looper.java:164)
          at android.app.ActivityThread.main(ActivityThread.java:6494)
          at java.lang.reflect.Method.invoke(Native Method)
          at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
          at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
  </code></pre>
  
  <p>EDIT: I found some interesting staff in the sourcecode. This application is working with the ros-library. I found this in the my programm:  </p>
  
  <pre><code>public class ControlActivity extends RosActivity{
  public ControlActivity() {
      super("RosAndroidExample", "RosAndroidExample");
  }
  </code></pre>
  
  <p>This part of the code make the notification, but i dont know what i can do, to solve this problem</p>
  
  <p>I hope this is enough information to solve my problem. When you need any kind of infomation please let me know. </p>