Identical to `PluginSet.handle`, except:

    #. If this plugin set is empty, `object` is returned as-is.
    #. If any plugin returns ``None``, it is returned without
       calling any further plugins.

def filter(self, object, *args, **kw):
    '''
    Identical to `PluginSet.handle`, except:

    #. If this plugin set is empty, `object` is returned as-is.
    #. If any plugin returns ``None``, it is returned without
       calling any further plugins.
    '''
    for plugin in self.plugins:
      object = plugin.handle(object, *args, **kw)
      if object is None:
        return object
    return object