title: Crash report from a user. How can I solve this crash?
body: <p>I uploadet my app yesterday and now a user sended me a crash report.
  Here is the report:</p>
  
  <pre><code>java.lang.RuntimeException: Unable to pause activity {com.aaron.waller.angelasoundboard/com.aaron.waller.angelasoundboard.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.pause()' on a null object reference
      at android.app.ActivityThread.performPauseActivity(ActivityThread.java:4591)
      at android.app.ActivityThread.performPauseActivity(ActivityThread.java:4550)
      at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:4525)
      at android.app.ActivityThread.access$1300(ActivityThread.java:222)
      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1806)
      at android.os.Handler.dispatchMessage(Handler.java:102)
      at android.os.Looper.loop(Looper.java:158)
      at android.app.ActivityThread.main(ActivityThread.java:7229)
      at java.lang.reflect.Method.invoke(Native Method)
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)
  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.media.MediaPlayer.pause()' on a null object reference
      at com.aaron.waller.angelasoundboard.MainActivity.onPause(MainActivity.java:145)
      at android.app.Activity.performPause(Activity.java:7033)
      at android.app.Instrumentation.callActivityOnPause(Instrumentation.java:1339)
      at android.app.ActivityThread.performPauseActivity(ActivityThread.java:4577)
      ... 10 more
  </code></pre>
  
  <p>The onPause() method is doing problems, is that right?
  What can I do now?</p>