code: public static final Function<String, String> substringBetween(final String open, final String close) {
          return new SubStringBetween(open, close);
      }
docs: <p>
  Returns the substring between open and close or null if there is no match. It calls
  {@link StringUtils#substringBetween(String, String, String)}
  </p>
  
  @param open the String before the substring, may be null
  @param close the String after the substring, may be null
  @return the substring, null if no match