Reproduction of the problem
- Open dojo at https://dojo.telerik.com/@GaloisGirl/AqotEtep
- Click "Add expression" and pick "Product name", "Is not equal to", "".
- Click "Apply". The grid show 77 items, as expected.
- Click "Add group" and then "Apply".
The grid shows 0 items. The expression preview is (Product Name Is not equal to '').
The grid should show 77 items. For an optimal user experience, the empty groups should be deleted when applying the filter.