docs: public static void join(final StringBuilder buf, final String addAtBeginning, final String sep,
              final String addAtEnd, final Iterable<?> iterable) {
          if (!addAtBeginning.isEmpty()) {
              buf.append(addAtBeginning);
          }
          boolean first = true;
          for (final Object item : iterable) {
              if (first) {
                  first = false;
              } else {
                  buf.append(sep);
              }
              buf.append(item.toString());
          }
          if (!addAtEnd.isEmpty()) {
              buf.append(addAtEnd);
          }
      }