code: public static Opt<String> getNonEmptyString(String str) {
          return Opt.ofNullable(emptyToNull(str.trim()));
      }
docs: Transforms an all-whitespace string to an {@code absent} value.
  
  @param str String to check.
  @return A {@code present} containing the trimmed string, if the string had any non-whitespace character,
  or an {@code absent} value otherwise.