code: func (r *registry) Lookup(handlerType HandlerType) interface{} {
  	if handlerType == Auth {
  		return r.filters
  	} else if handlerType == Decoration {
  		return r.decorators
  	} else if handlerType == Endorsement {
  		return r.endorsers
  	} else if handlerType == Validation {
  		return r.validators
  	}
  
  	return nil
  }
docs: // Lookup returns a list of handlers with the given
  // given type, or nil if none exist