code: @Override
    protected String resolveCodeWithoutArguments(String code, @Nullable @CheckForNull Locale locale) {
      Stream<Locale> candidates = Stream.of(locale, tryGetFallbackLocale(), DEFAULT_LOCALE);
      return candidates
          .filter(Objects::nonNull)
          .map(candidate -> messageRepository.resolveCodeWithoutArguments(code, candidate))
          .filter(Objects::nonNull)
          .findFirst()
          .orElse(null);
    }
docs: Looks up a code in the {@link MessageResolution}.
  
  <p>First tries the given locale if it is nonnull, then the fallbackLocale and finally the
  default locale.
  
  @param code the messageID to look up.
  @param locale the Locale whose language code should be tried first, may be null
  @return The message, or null if none found.