Within an IAM policy, can you add an IfExists condition at the end of a Null condition?

A.
Yes, you can add an IfExists condition at the end of a Null condition but not in all Regions.

B.
Yes, you can add an IfExists condition at the end of a Null condition depending on the condition.

C.
No, you cannot add an IfExists condition at the end of a Null condition.

D.
Yes, you can add an IfExists condition at the end of a Null condition.

Explanation:
Within an IAM policy, IfExists can be added to the end of any condition operator except the Null
condition. It can be used to indicate that conditional comparison needs to happen if the policy key
is present in the context of a request; otherwise, it can be ignored.
http://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_elements.html