code: public ResultsMap<String, List<Certification>> getMoviesCertification() throws MovieDbException {
          URL url = new ApiUrl(apiKey, MethodBase.CERTIFICATION).subMethod(MethodSub.MOVIE_LIST).buildUrl();
          String webpage = httpTools.getRequest(url);
  
          try {
              JsonNode node = MAPPER.readTree(webpage);
              Map<String, List<Certification>> results = MAPPER.readValue(node.elements().next().traverse(), new TypeReference<Map<String, List<Certification>>>() {
              });
              return new ResultsMap<>(results);
          } catch (IOException ex) {
              throw new MovieDbException(ApiExceptionType.MAPPING_FAILED, "Failed to get movie certifications", url, ex);
          }
      }
docs: Get a list of movies certification.
  
  @return
  @throws MovieDbException