Need to have Response Answer and Response text in same column

Summary:

Dear Experts,

Please advise that my questionnaire consists of both response text and response answers. 

Some response answers will be blank when the question is required in the response text.

When I ran the report I am getting more blanks in response-text. I need to have that response text in the response answer column itself. Which means I only need to know the response.

I tried with the below CASE expression but had no luck. Please advise what am missing.

" IFNULL(CAST("Checklist Questionnaire"."Response Answer" AS CHAR), CAST("Checklist Questionnaire"."Response Text" AS CHAR)) "

When I use the above expression I got the below error.