code: public static void callOnPriorityChanged(@Nullable List<ProducerContextCallbacks> callbacks) {
      if (callbacks == null) {
        return;
      }
      for (ProducerContextCallbacks callback : callbacks) {
        callback.onPriorityChanged();
      }
    }
docs: Calls {@code onPriorityChanged} on each element of the list. Does nothing if list == null