code: def release(cls, entity, unit_of_work):
          
          if not hasattr(entity, '__everest__'):
              raise ValueError('Trying to unregister an entity that has not '
                               'been registered yet!')
          elif not unit_of_work is entity.__everest__.unit_of_work:
              raise ValueError('Trying to unregister an entity that has been '
                               'registered with another session!')
          delattr(entity, '__everest__')
docs: Releases the given entity from management under the given Unit Of
          Work.
  
          :raises ValueError: If `entity` is not managed at all or is not
            managed by the given Unit Of Work.