code: public static Object keyValue(Object entity) {
  		Class<?> clazz = entity.getClass();
  		Field key = fields.get(clazz);
  		
  		try {
  			if (key == null) {
  				return keyField(clazz).get(entity);
  			} else {
  				return key.get(entity);
  			}
  			
  		} catch (IllegalAccessException e) {
  			throw new UncheckedException(e);
  		}
  	}
docs: Returns key value of the specified entity instance.
  
  @param entity An entity instance.
  @return The id value of the specified entity instance.