[VOTE] PIP-318: Don't retain null-key messages during topic compaction

[Cong Zhao]

Hi Community,

This thread is to start a vote for PIP-318.

PIP: https://github.com/apache/pulsar/pull/21541
Discussion thread: 
https://lists.apache.org/thread/68k6vrghfp3np601lrfx5mbfmghbbrjh

Thanks,
Cong Zhao