code: @Override
  	public Object evaluate(Message message) throws JMSException
      {
          Object operandValue = operand.evaluate(message);
          return operandValue == null ? Boolean.TRUE : Boolean.FALSE;
      }
docs: /*
  (non-Javadoc)
  @see net.timewalker.ffmq4.common.message.selector.expression.SelectorNode#evaluate(javax.jms.Message)