code: public SingleFieldBuilder<MType, BType, IType> setMessage(
        MType message) {
      if (message == null) {
        throw new NullPointerException();
      }
      this.message = message;
      if (builder != null) {
        builder.dispose();
        builder = null;
      }
      onChanged();
      return this;
    }
docs: Sets a  message for the field replacing any existing value.
  
  @param message the message to set
  @return the builder