code: public Long getLong (String key, Supplier<Long> notFound) {
          return getParsed (key, Long::new, notFound);
      }
docs: Retrieve a mapped element and return it as a Long.
  
  @param key A string value used to index the element.
  @param notFound A function to create a new Long if the requested key was not found
  @return The element as a Long, or notFound if the element is not found.