code: public org.geolatte.geom.Geometry evaluate(Object o) {
  
          EntityClassReader classReader = EntityClassReader.getClassReaderFor(o.getClass(), null, "id");
          Object result = null;
          try {
              result = classReader.getPropertyValue(o, propertyName);
          }
          catch (InvalidObjectReaderException e) {
              ; // can never occur
          }
  
          if (!(result instanceof Geometry))
                  return null;
  
          return (Geometry)result;
      }
docs: Evaluates the given object against this expression.
  
  
  @param o The object to evaluate.
  @return True if the given object matches this expression, false otherwise.