docs: public static String join(final Collection<?> collection, final String separator) {
          StringBuffer buffer = new StringBuffer();
          boolean first = true;
          Iterator<?> iter = collection.iterator();
          while (iter.hasNext()) {
              Object next = iter.next();
              if (first) {
                  first = false;
              } else {
                  buffer.append(separator);
              }
              buffer.append(next);
          }
          return buffer.toString();
      }