docs: public static Map<String, String> getSubmap(Map<String, String> mapIn, String subkey) {
          if (mapIn == null || mapIn.isEmpty()) {
              return Collections.emptyMap();
          }
          // Get map sub-element.
          return mapIn.entrySet().stream()
                  .filter(entry -> entry.getKey().toLowerCase().startsWith(subkey.toLowerCase()))
                  .map(entry -> {
                      String newKey = entry.getKey().substring(subkey.length(), entry.getKey().length());
                      return new AbstractMap.SimpleImmutableEntry<>(newKey, entry.getValue());
                  })
                  .collect(Collectors.toMap(Entry::getKey, Entry::getValue));
      }