@Contract(pure = true)
  public static @Nullable String joinOrNull(String @NotNull ... args) {
    StringBuilder r = new StringBuilder();
    for (String arg : args) {
      if (arg == null) return null;
      r.append(arg);
    }
    return r.toString();
  }
@Contract(pure = true)
  public static @Nullable String joinOrNull(String @NotNull ... args)