The suspend-state attribute def says the attribute is required, but if the SuspendController service is not up it returns undefined.

This can primarily happen if the value is read while the server is shutting down, e.g. https://ci.wildfly.org/viewLog.html?buildId=90460&buildTypeId=WildFlyCore_PullRequest

Since we have graceful startup implemented, I think SUSPENDED is a correct value if the suspend controller is not present. If we're booting and the suspend controller isn't installed yet, it's suspended. And once we get to the point in shutdown where the SC is gone, it's last state was SUSPENDED.