In the query editor today, you can’t do things like “{Parameter} equals (empty value)”. You always have to choose a data column when you filter, you can’t choose a parameter direclty.
It would be good to enable this because in this case we could handle optional parameter : a parameter becomes optional if you say “your_column equals {Parameter} OR {Parameter} equals (empty value)”.
That can’t be done today.
Well with SQL Expression you can handle that but you know users are not always SQL experts.