public static void join(@NotNull Collection<String> strings, @NotNull String separator, @NotNull StringBuilder result) {
    boolean isFirst = true;
    for (String string : strings) {
      if (string != null) {
        if (isFirst) {
          isFirst = false;
        }
        else {
          result.append(separator);
        }
        result.append(string);
      }
    }
  }
public static void join(@NotNull Collection<String> strings, @NotNull String separator, @NotNull StringBuilder result)