@Deprecated
  @ApiStatus.ScheduledForRemoval
  @Contract(pure = true)
  public static @Unmodifiable @NotNull <T> Set<T> set(T t) {
    return Collections.singleton(t);
  }
@Deprecated
  @ApiStatus.ScheduledForRemoval
  @Contract(pure = true)
  public static @Unmodifiable @NotNull <T> Set<T> set(T t)