Prio high, because it is a reproducible crash. And crashes should always get higher prio.

To reproduce this it is very simple.

1. export GNUPGHOME=$(mktemp -d)
2. Run kleopatra and gererate a key
3. Select revoke certification.

It is already viewable that the keyselectioncombo at the top is empty. If you still confirm you get a crash:

gpg_revsig (flags=0, userid=0x7fffc4002640 "Andre Heinecke <andre.heinecke@intevation.de>", signing_key=0x0, 
    key=<optimized out>, engine=0x7fffc40023a0) at ../../../src/gpgme/src/engine-gpg.c:3308
3308        err = add_arg (gpg, signing_key->fpr);