code: public final Number evaluateNumeric( Message message ) throws JMSException
      {
          Object value = evaluate(message);
          if (value == null)
              return null;
   
          if (value instanceof Number)
              return ArithmeticUtils.normalize((Number)value);
          
          throw new FFMQException("Expected a numeric but got : "+value.toString(),"INVALID_SELECTOR_EXPRESSION");
      }
docs: Evaluate this node as a number