code: func (f *Function) hookClean() error {
  	for _, name := range f.Plugins {
  		if p, ok := plugins[name].(Cleaner); ok {
  			if err := p.Clean(f); err != nil {
  				return err
  			}
  		}
  	}
  	return nil
  }
docs: // hookClean calls Cleaners.