Web Apps `value` is sometimes `null`

I opened an issue on the azure SDK for python (https://github.com/Azure/azure-sdk-for-python/issues/32993), since that is where I observed it, but they directed me here. Like the title here mentions, the `value` field ([here](https://github.com/Azure/azure-rest-api-specs/blob/42e2c0bcd77b0de6c523404668fa63511484d485/specification/web/resource-manager/Microsoft.Web/stable/2022-09-01/WebApps.json#L24708-L24714)) is sometimes `null`, which causes the SDK to throw an exception. The original issue has more details.

Start with the WebApps.json schema at lines 24708-24714 and read the linked Azure SDK for Python issue for the observed null response details. Determine how the REST specification should represent a null value so generated SDK consumers do not throw an exception, then verify the specification change against that reported behavior.

Written by the indexing model from the issue text.