code: protected AbstractMessageContentBuilder getMessageContentBuilder() {
          if (getAction().getMessageBuilder() != null && getAction().getMessageBuilder() instanceof AbstractMessageContentBuilder) {
              return (AbstractMessageContentBuilder) getAction().getMessageBuilder();
          } else {
              PayloadTemplateMessageBuilder messageBuilder = new PayloadTemplateMessageBuilder();
              getAction().setMessageBuilder(messageBuilder);
              return messageBuilder;
          }
      }
docs: Get message builder, if already registered or create a new message builder and register it
  
  @return the message builder in use