code: @Nonnull
      public static String join(@Nonnull Iterable<String> elements, @Nonnull String delimiter) {
          StringBuilder result = new StringBuilder();
          Iterator<String> it = elements.iterator();
          while (it.hasNext()) {
              String element = it.next();
              result.append(element);
              if (it.hasNext()) {
                  result.append(delimiter);
              }
          }
          return result.toString();
      }
docs: Concatenate the given {@code elements} using the given {@code delimiter} to concatenate.