code: function defaultPushCallback(error, pushMessage) {
      if (error) {
          diag.debug.error('push failure', error);
      }
      else if (pushMessage && pushMessage.message) {
          diag.debug.info('push received', pushMessage.message);
      }
      return pushMessage;
  }
docs: default implementation of PushCallback reporting errors and incoming messages to the console.
  
  @param error cause of failure.
  @param pushMessage incoming notification data.
  
  @return {PushMessage} same value as parameter causing confirmation of message.