ForAnyValue:Null
ForAnyValue: Null
ForAnyValue:
Null
is technically something you can put in a policy, but never should. I'm not even sure what it would do and I'm not going to check. If Jeff Barr sends you an email titled "How ya doin buddy?" and asks how things are going at home, it's because AWS support found this in one of your policies and they are worried about you.
You can NOT use policy variables in the value of this operator.