This is a simple generator for enumerating data types in UNION SELECT NULL,NULL -- based SQLi attacks. I've tried to find a way of doing this through Burp's intruder, but could not figure it out. So I've just wrote this simple script to do it for me.
1 - Download the generator.py script
2 - Navigate to the directory where you've downloaded it to
3 - python3 generator.py
4 - How many positions - This defines, how many positions will be generated. If you choose 3, the output will be as follows:
5 - Character(s) to substitute - This defines what will be substituted instead of the NULL character.
6 - How many substitutions: - How many substitutions will be used per line. If you use 2 for example, the output will look like this:


