public static <T> void join(@NotNull Iterable<? extends T> items,
                              @NotNull Function<? super T, ? extends CharSequence> f,
                              @NotNull String separator,
                              @NotNull StringBuilder result) {
    Strings.join(items, f, separator, result);
  }
public static <T> void join(@NotNull Iterable<? extends T> items,
                              @NotNull Function<? super T, ? extends CharSequence> f,
                              @NotNull String separator,
                              @NotNull StringBuilder result)