docs: public static <T> String join(final Iterable<T> iterable, final String separator) {
          final StringBuilder sb = new StringBuilder();
          int index = 0;
          for (final T item : iterable) {
              if (index > 0) {
                  sb.append(separator);
              }
              sb.append(item.toString());
              index += 1;
          }
          return sb.toString();
      }