code: protected Double eval(final Object[] _value)
      {
          final Double ret;
  
          if (_value == null) {
              ret = null;
          } else if ((_value[0] instanceof String) && (((String) _value[0]).length() > 0)) {
              ret = Double.parseDouble((String) _value[0]);
          } else if (_value[0] instanceof Number) {
              ret = ((Number) _value[0]).doubleValue();
          } else  {
              ret = null;
          }
  
          return ret;
      }
docs: Evaluate the value.
  @param _value value to be evaluated
  @return Long value