docs: public static Set<String> getLocalizationProblems( Class<?> i18nClass,
                                                         Locale locale ) {
          CheckArg.isNotNull(i18nClass, "i18nClass");
          Map<Class<?>, Set<String>> classToProblemsMap = LOCALE_TO_CLASS_TO_PROBLEMS_MAP.get(locale == null ? Locale.getDefault() : locale);
          if (classToProblemsMap == null) {
              return Collections.emptySet();
          }
          Set<String> problems = classToProblemsMap.get(i18nClass);
          if (problems == null) {
              return Collections.emptySet();
          }
          return problems;
      }