code: public static Object toGUId(Object o) throws PageException {
  	String str = toString(o);
  	if (!Decision.isGUId(str)) throw new ExpressionException("can't cast [" + str + "] to guid value");
  	return str;
      }
docs: cast a Object to a GUID
  
  @param o Object to cast
  @return casted Query Object
  @throws PageException