code: public EntityManager createEntityManager(String projectId, InputStream jsonCredentialsStream) {
      return createEntityManager(projectId, jsonCredentialsStream, null);
    }
docs: Creates and return a new {@link EntityManager} using the provided JSON formatted credentials.
  
  @param projectId
  the project ID
  
  @param jsonCredentialsStream
  the JSON formatted credentials for the target Cloud project.
  @return a new {@link EntityManager}