code: @Override
  	public Object evaluate(Message message) throws JMSException
      {
          Number value = operand.evaluateNumeric(message);
          if (value == null)
              return null;
          
          return ArithmeticUtils.minus(value);
      }
docs: /*
  (non-Javadoc)
  @see net.timewalker.ffmq4.common.message.selector.expression.SelectorNode#evaluate(javax.jms.Message)