Program: 35601
Project: 35601
Buggy source:
@Override protected void onQuery(@Nullable CharSequence query){
  if (query != null && query.length() > 0) {
    UserEntity currentUser=userUtils.getCurrentUser();
    adapter.setFilter(query.toString());
    ncApi.getMentionAutocompleteSuggestions(ApiUtils.getCredentials(currentUser.getUserId(),currentUser.getToken()),ApiUtils.getUrlForMentionSuggestions(currentUser.getBaseUrl(),roomToken),query.toString(),null).subscribeOn(Schedulers.newThread()).observeOn(AndroidSchedulers.mainThread()).retry(3).subscribe(new Observer<MentionOverall>(){
      @Override public void onSubscribe(      Disposable d){
      }
      @Override public void onNext(      MentionOverall mentionOverall){
        List<Mention> mentionsList=mentionOverall.getOcs().getData();
        List<AbstractFlexibleItem> internalUserItemList=new ArrayList<>();
        if (mentionsList.size() == 0 || (mentionsList.size() == 1 && mentionsList.get(0).getId().equals(query.toString()))) {
          userItemList=new ArrayList<>();
          adapter.notifyDataSetChanged();
        }
 else {
          for (          Mention mention : mentionsList) {
            internalUserItemList.add(new MentionAutocompleteItem(mention.getId(),mention.getLabel(),currentUser));
          }
          userItemList=internalUserItemList;
          adapter.updateDataSet(internalUserItemList,true);
        }
      }
      @Override public void onError(      Throwable e){
        userItemList=new ArrayList<>();
        adapter.updateDataSet(new ArrayList<>(),false);
      }
      @Override public void onComplete(){
      }
    }
);
  }
 else {
    userItemList=new ArrayList<>();
    adapter.updateDataSet(new ArrayList<>(),false);
  }
}

Fixed version (ground truth):
@Override protected void onQuery(@Nullable CharSequence query){
  if (query != null && query.length() > 0) {
    UserEntity currentUser=userUtils.getCurrentUser();
    adapter.setFilter(query.toString());
    ncApi.getMentionAutocompleteSuggestions(ApiUtils.getCredentials(currentUser.getUserId(),currentUser.getToken()),ApiUtils.getUrlForMentionSuggestions(currentUser.getBaseUrl(),roomToken),query.toString(),null).subscribeOn(Schedulers.newThread()).observeOn(AndroidSchedulers.mainThread()).retry(3).subscribe(new Observer<MentionOverall>(){
      @Override public void onSubscribe(      Disposable d){
      }
      @Override public void onNext(      MentionOverall mentionOverall){
        List<Mention> mentionsList=mentionOverall.getOcs().getData();
        List<AbstractFlexibleItem> internalUserItemList=new ArrayList<>();
        if (mentionsList.size() == 0 || (mentionsList.size() == 1 && mentionsList.get(0).getId().equals(query.toString()))) {
          adapter.notifyDataSetChanged();
        }
 else {
          for (          Mention mention : mentionsList) {
            internalUserItemList.add(new MentionAutocompleteItem(mention.getId(),mention.getLabel(),currentUser));
          }
          adapter.updateDataSet(internalUserItemList,true);
        }
      }
      @Override public void onError(      Throwable e){
        adapter.updateDataSet(new ArrayList<>(),false);
      }
      @Override public void onComplete(){
      }
    }
);
  }
 else {
    adapter.updateDataSet(new ArrayList<>(),false);
  }
}