code: func (s *MemoryUserStore) Load(id msp.IdentityIdentifier) (*msp.UserData, error) {
  	cert, ok := s.store[id.ID+"@"+id.MSPID]
  	if !ok {
  		return nil, msp.ErrUserNotFound
  	}
  	userData := msp.UserData{
  		ID:                    id.ID,
  		MSPID:                 id.MSPID,
  		EnrollmentCertificate: cert,
  	}
  	return &userData, nil
  }
docs: // Load loads a user from store