I miss the option for "none" and "any" when I filter for (not required text) custom fields.

In Redmine I had "none" and "any" for text and dropdown fields. I miss it in OpenProject  especially for non-required "Date" and "Text" fields. It does work for non-required "List", "Number" or "User" fields. It would also be good to have a tri-state boolean (i.e. "none" for not yet decided).