[Bug]: Firestore Connector can have empty cursors resulting in an incorrect success

[alexbeltran]

What happened?

Reproduction Steps:

1. Have a sufficiently large RunQuery that times out
2. Run query
3. The Connector terminates after timeout but returns a success.

This is likely due to, https://github.com/apache/beam/blob/master/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/firestore/FirestoreV1ReadFn.java#L426 which uses a last received value to get a start point. There is no error check so the last received value may be empty. From there an empty cursor is created.

Issue Priority

Priority: 2

Issue Component

Component: io-java-gcp

[chamikaramj]

Fixed by #22175