PGConnection.getNotifications(0) doesn't block

Hello.

I'm implementing a bit that is expected to wait for published channel
notifications,
and once there are any - process them.

I'm using PGConnection.getNotifications(0), but that immediately
returns an empty
array, and doesn't block like JavaDoc says it should.

I'm on 42.6.0.

What am I missing?

Thank you.