code: func IsEmpty(requestsToContexts RequestContextMapper) (bool, error) {
  	if requestsToContexts, ok := requestsToContexts.(*requestContextMap); ok {
  		return len(requestsToContexts.contexts) == 0, nil
  	}
  	return true, errors.New("Unknown RequestContextMapper implementation")
  }
docs: // IsEmpty returns true if there are no contexts registered, or an error if it could not be determined. Intended for use by tests.