#vulnerable code 
                              @Override
  public Set<T> current() {
    ImmutableSet.Builder<T> records = ImmutableSet.builder();
    for (final ChangeNotifier<T> changeNotifier : changeNotifiers) {
      records.addAll(changeNotifier.current());
    }
    return records.build();
  } 
                            #location 2 
                            #vulnerability type CHECKERS_IMMUTABLE_CAST
#fixed code
                              @Override
  public Set<T> current() {
    return records;
  }