title: android uiautomator cause "unfortunately, settings has stopped" error
body: <pre><code>    getUiDevice().pressHome();      
      new UiObject(new UiSelector().description("Apps")).click(); 
      new UiObject(new UiSelector().text("Apps")).click();        
      new UiScrollable(new UiSelector().scrollable(true)).setAsHorizontalList().scrollIntoView(new UiSelector().text("Settings"));
      new UiObject(new UiSelector().text("Settings")).click();
      new UiScrollable(new UiSelector().scrollable(true)).scrollTextIntoView("Accessibility");        
      new UiObject(new UiSelector().text("Accessibility")).click();
  </code></pre>
  
  <p>The finall line of code cuase the following error on my Nexus 4, i tried to google it, but can't find any related information, so can anybody help explain why the error happend?</p>
  
  <pre><code>10-23 13:43:16.466: E/AndroidRuntime(7995): FATAL EXCEPTION: main
  10-23 13:43:16.466: E/AndroidRuntime(7995): java.lang.RuntimeException: Unable to resume activity {com.android.settings/com.android.settings.SubSettings}: java.lang.NullPointerException
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2790)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2819)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2266)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.os.Handler.dispatchMessage(Handler.java:99)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.os.Looper.loop(Looper.java:137)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.ActivityThread.main(ActivityThread.java:5103)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at java.lang.reflect.Method.invokeNative(Native Method)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at java.lang.reflect.Method.invoke(Method.java:525)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at dalvik.system.NativeStart.main(Native Method)
  10-23 13:43:16.466: E/AndroidRuntime(7995): Caused by: java.lang.NullPointerException
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at com.android.settings.AccessibilitySettings.loadInstalledServices(AccessibilitySettings.java:586)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at com.android.settings.AccessibilitySettings.onResume(AccessibilitySettings.java:196)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.Fragment.performResume(Fragment.java:1738)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:919)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1057)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1039)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.FragmentManagerImpl.dispatchResume(FragmentManager.java:1850)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.Activity.performResume(Activity.java:5221)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2780)
  10-23 13:43:16.466: E/AndroidRuntime(7995):     ... 12 more
  </code></pre>