Using single and double quotes in an expression in PSQuery

I am creating custom queries in PS Query in tool 8.51 and in one case, I am creating a case statement.

I am testing for NULL and for ' ' (space) and after the END statement I want to include AS "DEPT_ID" so that my SQL is generated accurately.

PS Query will not let me use both single and double quotes, even tho it is required in this case for the Oracle SQL to come out correct.

How do I use both single and double quotes in my expression? Has any done anything similar and found a work around?

2nd part of question is then it does not appear when I use the AS "DEPT_ID" (omitting the ' ' for testing) other expressions, referring to the field name "DEPT_ID" (yes, I used it as a field name and edited the field so the title was DEPT_ID and the unique name is DEPT_ID as well) it does not find that DEPT_ID is a valid column name.