Method unmodifiableMap

guava/src/com/google/common/collect/Maps.java:585–592

(
      Map<K, ? extends V> map)

  }

  private static <K extends @Nullable Object, V extends @Nullable Object> Map<K, V> unmodifiableMap(
      Map<K, ? extends V> map) {
    if (map instanceof SortedMap) {
      return Collections.unmodifiableSortedMap((SortedMap<K, ? extends V>) map);
    } else {
      return Collections.unmodifiableMap(map);
    }
  }

  private static class MapDifferenceImpl<K extends @Nullable Object, V extends @Nullable Object>
      implements MapDifference<K, V> {