The AWS region where this access key was most recently used. This field is null when:
The user does not have an access key. An access key exists but has never been used, at least not since IAM started
tracking this information on April 22nd, 2015.
There is no sign-in data associated with the user For more information about AWS regions, see Regions and Endpoints (http://docs.aws.amazon.com/general/latest/gr/rande.html)
in the Amazon Web Services General Reference.