Quick thought, use the NULLIF function

😎

USE tempdb;

GO

DECLARE @test-2 TABLE (STR_VAL VARCHAR(50) NOT NULL);

INSERT INTO @test-2(STR_VAL) VALUES ('ABC'),('DEF'),('NULL'),('JKL'),('NULL');

SELECT

T.STR_VAL

,NULLIF(T.STR_VAL,'NULL') AS STR_VAL_NULL

FROM @test-2 T

Results

STR_VAL STR_VAL_NULL

-------- ------------

ABC ABC

DEF DEF

NULL NULL

JKL JKL

NULL NULL