In T305406: Newcomer tasks: quick analysis of AND selection usage, we learned that a significant number of users end up selecting multiple topics in AND mode, such that zero results are found. We should disable the "Save" button in topic dialog, so that the user can't end up in a no results state.
We should also add a "Change to "match all" filters" button on the no results screen if the Match ALL filter is selected, so that users can easily change by selecting that call-to-action.