private static @NotNull FSRecordsImpl implOrFail() {
    FSRecordsImpl _impl = impl;
    if (_impl == null) {
      throw new ServiceNotReadyException("VFS instance is not initialized yet");
    }
    else if (_impl.isClosed()) {
      //guaranteed to fail, and provides diagnostic:
      _impl.checkNotClosed();
    }

    return _impl;
  }
private static @NotNull FSRecordsImpl implOrFail()