Handle topics set to empty dict

[therve]

The doc already points to {} instead of None for retrieving the topics,
let's check both.

[codecov]

Codecov Report

Merging #4974 into master will decrease coverage by 11.82%.
The diff coverage is 0%.

Impacted Files	Coverage Δ
...er/datadog_checks/kafka_consumer/kafka_consumer.py	68.18% <0%> (ø)
...checks_dev/tests/plugin/test_environment_runner.py
riakcs/datadog_checks/riakcs/riakcs.py
oracle/tests/test_oracle.py
...r/datadog_checks/openstack_controller/__about__.py
twistlock/datadog_checks/twistlock/twistlock.py
linkerd/datadog_checks/linkerd/linkerd.py
...oller/datadog_checks/openstack_controller/utils.py
istio/tests/test_e2e.py
gitlab_runner/tests/test_integration.py
... and 836 more

[jeffwidman]

It's been a little while, so my memory is hazy, but I recall this being a purposeful design choice so that a user can say "I want to get only the broker highwater offsets associated with these consumer groups, w/o getting the consumer offsets".

With this change, I don't think that's possible? To be clear, I have no objections to this change, just wanted to mention the original intent here.

Again, it's been a while since I wrote this so I may be completely misremembering.

Similar thing I think (but am not sure) applies to #5035.