How to fix Filter doesn't work if I remove chars

I've implemented filter function inside my adapter, with DiffUtil.

As for now - the filter works, the problem is that if I remove chars from the search, It's just return empty list.

How can I solve this problem?

my filter function:

   @Override
    public Filter getFilter() {
        return new Filter() {
            @Override
            protected FilterResults performFiltering(CharSequence constraint) {
                List<Cars> listResult;
                if (constraint.length() == 0) {
                    listResult = getCurrentList();
                } else  {
                    listResult = getFilteredResults(constraint.toString().toLowerCase());
                }

                FilterResults results = new FilterResults();
                results.values = listResult;
                Log.i("filter", "results results.values" + results.values);

                return results;
            }

            @SuppressWarnings("unchecked")
            @Override
            protected void publishResults(CharSequence constraint, FilterResults results) {
                Log.i("filter", "publishResults started");
                submitList((List<Cars>)results.values);

            }
        };
    }

getFilterResults:
    private List<Cars> getFilteredResults(String constraint) {
        List<Cars> results = new ArrayList<>();
        for (Cars item : getCurrentList()) {
            if (item.getTitle().toLowerCase().contains(constraint)) {
                results.add(item);
            }
        }
        return results;
    }

UPDATE: i might have been spotted the issue - I've newList variable the that suppose to save the original list. I'm initilaze this in the constructor like this:

this.newList = getCurrentList()

but getCurrentList() return empty list.