@NotNull
  public String getSeparator(final ResourceBundle resourceBundle) {
    if (!(resourceBundle instanceof ResourceBundleImpl resourceBundleImpl)) {
      return ".";
    }
    String separator = myUserDefinedSeparators.getSeparators().get(resourceBundleImpl.getUrl());
    return separator == null ? Objects.requireNonNull(myGuessedSeparators.get(resourceBundleImpl)) : separator;
  }
@NotNull
  public String getSeparator(final ResourceBundle resourceBundle)