I'm sorry for not being specific. I will have to update the description so that it won't cause confusion like #6838 (comment).

$ printf '<13>Sep 15 15:07:58 HOST: null\0here' | nc -w1 -u -U /run/systemd/journal/dev-log

$ journalctl -t HOST -o verbose
...
    MESSAGE=null

From #1460

Of course, this will make the patch more complicated, as this means we have to patch much further down to ensure we always keep the ptr+length bit intact.