Peering: backend will "silently" remove subscription from registration list

Sometimes the peering API will raise some error like below:

> "Subscription is not registered with the resource provider."

As we discussed with service team, this issue happens because:

> Currently when service get upgraded, it will clear subscription data if that subscription has no associated peerASN. A later incoming "CREATE" invocation will populate subscription data back.

While in terraform, as we have to check whether the resource going to be created already exist, we need to firstly call "GET". In this case, it will fail (complaining not registered) if the subscription has no peerASN associated.

I wonder if it is possible to also populate the subscription data back on an incoming "GET" invocation?

The issue names no files, tests, or entry points. Start by locating the peering API's registration GET and CREATE definitions and compare how subscription data is handled; done means a GET invocation can restore the missing subscription data instead of failing with the registration error.

Written by the indexing model from the issue text.