code: public StorageBuilder setUserCredentialsRepository( UserCredentialsRepository userCredentialsRepo, String userId )
      {
          this.userCredentialsRepo = userCredentialsRepo;
          this.userId = userId;
  
          return this;
      }
docs: Set the user credentials repository. This setter must always be called during the build
  
  @param userCredentialsRepo The repository
  @param userId The user identifier (may be null if the identifier is unknown)
  @return The builder