docs: public static String join(int[] array, String separator) {
          if (array != null) {
              StringBuilder buf = new StringBuilder(Math.max(16, (separator.length() + 1) * array.length));
              char singleChar = separator.length() == 1 ? separator.charAt(0) : 0;
              for (int i = 0; i < array.length; i++) {
                  if (i != 0) {
                      if (singleChar != 0) {
                          // More efficient
                          buf.append(singleChar);
                      } else {
                          buf.append(separator);
                      }
                  }
                  buf.append(array[i]);
              }
              return buf.toString();
          } else {
              return "";
          }
      }