docs: public static <K, V> Map<K, V> mergeMap(final Map<K, V> localValue, final Map<K, V> defaultValue) {
          return Optional.ofNullable(localValue).map(v -> Optional.ofNullable(defaultValue).map(w -> {
              final Map<K, V> map = new LinkedHashMap<>(w);
              map.putAll(v);
              return map;
          }).orElse(localValue)).orElse(defaultValue);
      }