code: private String urlEncodeFilters(final Map<String, List<String>> filters) throws DockerException {
      try {
        final String unencodedFilters = objectMapper().writeValueAsString(filters);
        if (!unencodedFilters.isEmpty()) {
          return urlEncode(unencodedFilters);
        }
      } catch (IOException e) {
        throw new DockerException(e);
      }
      return null;
    }
docs: Takes a map of filters and URL-encodes them. If the map is empty or an exception occurs, return
  null.
  
  @param filters A map of filters.
  @return String
  @throws DockerException if there's an IOException