title: Exception in unbindDrawables
body: <p>Im getting null pointer exception in unbindDrawables where im Removing callbacks on all the background drawables. </p>
  
  <pre><code>protected void onDestroy() {
      super.onDestroy();
      unbindDrawables(findViewById(R.id.top_layout));
      Runtime.getRuntime().gc();
  }
  
  
  private void unbindDrawables(View view) {
      if (view.getBackground() != null) {
          view.getBackground().setCallback(null);
      }
      if (view instanceof ViewGroup) {
          for (int i = 0; i &lt; ((ViewGroup) view).getChildCount(); i++) {
  
              unbindDrawables(((ViewGroup) view).getChildAt(i));
          }
          try {
              ((ViewGroup) view).removeAllViews();
          } catch (UnsupportedOperationException  e) {
  
          }
      }
  }
  </code></pre>
  
  <p>Below is the log:</p>
  
  <pre><code>  02-27 15:11:05.286: E/AndroidRuntime(13549): FATAL EXCEPTION: main
  02-27 15:11:05.286: E/AndroidRuntime(13549): java.lang.RuntimeException: Unable to destroy activity {com.xxx.xxx.xxx/com.xxx.xxxx.xxxActivity}: java.lang.NullPointerException
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3655)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3673)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at android.app.ActivityThread.access$2900(ActivityThread.java:125)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at android.os.Handler.dispatchMessage(Handler.java:99)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at android.os.Looper.loop(Looper.java:123)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at android.app.ActivityThread.main(ActivityThread.java:4627)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at java.lang.reflect.Method.invokeNative(Native Method)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at java.lang.reflect.Method.invoke(Method.java:521)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at dalvik.system.NativeStart.main(Native Method)
  02-27 15:11:05.286: E/AndroidRuntime(13549): Caused by: java.lang.NullPointerException
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at com.xxx.xxx.xxx.unbindDrawables(xxxActivity.java:153)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at com.xxx.xxx.xxx.onDestroy(xxxActivity.java:141)
  02-27 15:11:05.286: E/AndroidRuntime(13549):    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3642)
  </code></pre>