private @Nullable Map<String, XmlTag> getIdMap() {
    final XmlFile file = getFile();

    if (file != null) {
      CachedValue<Map<String, XmlTag>> value = file.getUserData(ourCachedIdsKey);
      if (value == null) {
        value = CachedValuesManager.getManager(file.getProject()).createCachedValue(new MapCachedValueProvider(file), false);
        file.putUserData(ourCachedIdsKey, value);
      }

      return value.getValue();
    }
    return null;
  }
private @Nullable Map<String, XmlTag> getIdMap()