[FEATURE REQ] BlobChangeFeed client returns valid continuation token at the end of enumeration

[MalcolmMcNeely]

Library name

Azure.Storage.Blobs.ChangeFeed

Please describe the feature.

We want to use the blob change feed to enumerate all items one day and on another day continue the enumeration where we left off, so we don't enumerate the whole thing every time. Previously we relied on the continuation token returns by the enumerator and this looked to be in keeping with the documentation: https://learn.microsoft.com/en-us/azure/storage/blobs/storage-blob-change-feed-how-to#resume-reading-records-from-a-saved-position

However, going from version 12.0.0-preview.29 to 12.0.0-preview.52, the continuation token is now null at the end of enumeration. Rather than saving the last not-null token, or converting the whole project to access the change feed using date based mechanics, it would be great if we got a valid token at the end which we could use later.

Addendum: testing this out it seems that sometimes the enumerator returns a null continuation cursor, but at other times it doesn't. Would be great if this behaviour could be consistent.

[github-actions]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @xgithubtriage.