Under 0.11.2 I never had a problem creating a 0-tx fee. But after upgrading to 0.12, I always get the error "mempool min fee not set" when I try to send it. There's an ugly workaround of calling prioritisetransaction as described here: https://git.io/vabUJ. But that doesn't work if the mempool is already full, so I first have to restart the daemon to clear the mempool, before I can send the reprioritised tx.Is there a workaround that doesn't require restarting the daemon?