code: func (s *CertFileUserStore) Load(key msp.IdentityIdentifier) (*msp.UserData, error) {
  	cert, err := s.store.Load(storeKeyFromUserIdentifier(key))
  	if err != nil {
  		if err == core.ErrKeyValueNotFound {
  			return nil, msp.ErrUserNotFound
  		}
  		return nil, err
  	}
  	certBytes, ok := cert.([]byte)
  	if !ok {
  		return nil, errors.New("user is not of proper type")
  	}
  	userData := &msp.UserData{
  		MSPID:                 key.MSPID,
  		ID:                    key.ID,
  		EnrollmentCertificate: certBytes,
  	}
  	return userData, nil
  }
docs: // Load returns the User stored in the store for a key.