`Microsoft.Insights/Workbooks` returns `type` as null

Hi,

I am attempting to list resources in a subscription via the REST API and categorize things by the `type` field, but Microsoft.Insights/Workbooks sometimes returns null where the resource provider is usually listed for resources. This seems to be the case for all the API versions, including the newest stable 2023-06-01.

It's inconsistent and I can't determine what is causing it. Some workbooks return the type, others don't. All of these workbooks were created in 2022 and are all sourced to the same `Microsoft.OperationalInsights/Workspace` ID.

No source file or test is identified. Start by reproducing the subscription resource listing for Microsoft.Insights/Workbooks across the mentioned API versions, comparing workbooks whose type is present with those returning null. Done requires establishing whether the discrepancy is in the REST API specification or service response and defining the resulting correction.

Written by the indexing model from the issue text.