Case statement with Date timestamp field looking for NULL value

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I have written a formula to check for the2nd  interview date field and if it’s empty then assign ‘not filled out’ else enter that date. The formula syntax doesn’t give any errors but the report is not refreshing and showing any data.

Here is the formula I have written that saves without errors

CASE WHEN (CAST ("Submission Dates"."2nd Interviewed Date" AS DATE)) IS NULL THEN (CAST( 'Not filled out' AS DATE)) ELSE CAST ( "Submission Dates"."2nd Interviewed Date" AS DATE) END

Please point out what looks incorrect that might be causing my report to error out.