Presentation Variable name being passed as value

Question

I have a requirement where value needs to be checked against two separate fields for filtering (as OR statement). But there should be ability to filter on these fields separately as well.
Dashboard prompt:
Province [Multi search]
State [Multi search]
Combined search (Province OR State Fields) [Edit Box] --- used to pass presentation variable
Report filter:
Province is prompted
AND State is prompted
AND Province is @{presentation_variable} (no default)
OR State is @{presentation_variable} (no default)
But if the text field with presentation variable in not used to filter, then the report shows no result because the presentation variable name itself is taken as a value. Any solution how this can be done making sure that if province only is searched for then the presentation variable is not passed as value and the query returns no results?
Thanks everyone.

Answer 1

Thanks Rachit, that helps. For the scenario mentioned initially, even this works:
Province is @{presentation_variable} (no default)
OR State is @{presentation_variable} (no default)
But the challenge is if I want to add another filter (like country) also as a filter. When users filter only on country, then the report shows no results because no value has been passed to the presentation variable and the query generated uses presentation variable name as the value!