Two things.
First, your variable INCOME-CODE
actually has quotes in it. Try this short demonstration:
@echo off
set TEST1="this is a string with spaces"
set "TEST2=this is a string with spaces"
echo %TEST1%
echo %TEST2%
Second, you are comparing to the literal string "NULL". There is no NULL value in batch. Please see this post for more details: What is the proper way to test if variable is empty in a batch file... What you probably want to do is compare to an empty string or use one of the methods in the question above if you're working with something more complex.
IF "%INCOME-CODE%"=="" ( ... )