the log may cause NullPointerException

in class **RequestManagerRetriever**
```
@Override
public boolean handleMessage(Message message) {
boolean handled = true;
Object removed = null;
Object key = null;
switch (message.what) {
case ID_REMOVE_FRAGMENT_MANAGER:
android.app.FragmentManager fm = (android.app.FragmentManager) message.obj;
key = fm;
removed = pendingRequestManagerFragments.remove(fm);
break;
case ID_REMOVE_SUPPORT_FRAGMENT_MANAGER:
FragmentManager supportFm = (FragmentManager) message.obj;
key = supportFm;
removed = pendingSupportRequestManagerFragments.remove(supportFm);
break;
default:
handled = false;
break;
}
if (handled && removed == null && Log.isLoggable(TAG, Log.WARN)) {
Log.w(TAG, "Failed to remove expected request manager fragment, manager: " + key);
}
return handled;
}
```
the log print FragmentManager info, some extreme case ,removed may was null and the key`s mHost may was null too,and in this case the log may case NullPointerException