code: public static String trimToNull(String s) {
          s = trim(s);
          return isNotEmpty(s) ? s : null;
      }
docs: <p>
  Trims the specified string and, if the resulting string is empty, will return {@literal null} instead.
  </p>
  
  @param s
  the string to be trimmed (may be {@literal null})
  @return The trimmed {@code s} or {@literal null} if {@code s} is {@literal null} before or after being trimmed.