[BUG] Partition reset offset shows "null" for client ID

[MikeEdgar]

Describe the bug
The term "null" displays beside the group ID when resetting a consumer group's partition offset.

To Reproduce
Steps to reproduce the behavior:

1. Create a consumer group to a topic and produce messages to the topic
2. Disconnect the consumer
3. Navigate to reset the partition's offsets
4. After selecting the topic, observe the "null" member ID

Expected behavior
Nothing shown when no clients are actively consuming

Screenshots