boolean nullKeys = inverseFeatures.remove(MapFeature.ALLOWS_NULL_KEYS);
    boolean nullValues = inverseFeatures.remove(MapFeature.ALLOWS_NULL_VALUES);

    if (nullKeys) {
      inverseFeatures.add(MapFeature.ALLOWS_NULL_VALUES);
    }
    if (nullValues) {
      inverseFeatures.add(MapFeature.ALLOWS_NULL_KEYS);
    }

    inverseFeatures.add(NoRecurse.INVERSE);