code: @Override
    public synchronized void initFileSystemHelper(State state) throws FileBasedHelperException {
      if (fsHelper == null) {
        Credential credential = new GoogleCommon.CredentialBuilder(state.getProp(SOURCE_CONN_PRIVATE_KEY), state.getPropAsList(API_SCOPES))
                                                .fileSystemUri(state.getProp(PRIVATE_KEY_FILESYSTEM_URI))
                                                .proxyUrl(state.getProp(SOURCE_CONN_USE_PROXY_URL))
                                                .port(state.getProp(SOURCE_CONN_USE_PROXY_PORT))
                                                .serviceAccountId(state.getProp(SOURCE_CONN_USERNAME))
                                                .build();
  
        Drive driveClient = new Drive.Builder(credential.getTransport(),
                                              GoogleCommon.getJsonFactory(),
                                              credential)
                                     .setApplicationName(Preconditions.checkNotNull(state.getProp(APPLICATION_NAME), "ApplicationName is required"))
                                     .build();
        this.fsHelper = closer.register(new GoogleDriveFsHelper(state, driveClient));
      }
    }
docs: Initialize file system helper at most once for this instance.
  {@inheritDoc}
  @see org.apache.gobblin.source.extractor.filebased.FileBasedSource#initFileSystemHelper(org.apache.gobblin.configuration.State)