Checking if partitions list is empty before allocating a new list

[alexandredantas]

This check makes it possible to list all partitions assigned to a consumer group. In librdkafka, the method rd_kafka_ListConsumerGroupOffsets expects the partition to be NULL or having some content. However, in confluent-kafka-go a list is always created

[milindl]

Thanks a lot for submitting this PR!

Please also add unit tests to adminapi_test.go, one test case for nil topic partition list, which should fail in the unit test with "context deadline exceeded", and one test with 0-sized topic partition list, which should fail with "NULL or non-empty topic partition list must be passed".

Please let me know if you require any help with the changes.

[frankgrimes97]

@milindl I believe the requested changes have been addressed... are any further changes required before this can be reviewed, approved and merged? Thanks!

[milindl]

This looks good to me, mostly.
I created an internal branch with this change, and raised a PR, so that our CI can run and validate it once before we can merge it. #1007. I've also made some changes to the tests, mostly to the integration tests, and added the CHANGELOG.md entry.

[frankgrimes97]

@milindl Any update on this?

[milindl]

The internal PR is merged. Thanks for this! It'll be released with 2.2.0