Freeciv

This wasn't caught before because it's very rare. However, there may be ways to get units which are null in some situations like multiple build slots, etc. FCW server experienced it and had to fix it.

 static struct unit *city_create_unit(struct city *pcity,
                                      const struct unit_type *utype)
 {
   if (!pcity || !utype) return NULL;   // 17Oct2022 attempt to avoid segfault
 
   struct player *pplayer = city_owner(pcity);
   struct unit *punit;
   int saved_unit_id;
                       city_production_unit_veteran_level(pcity, utype),
                       pcity->id, 0);
   pplayer->score.units_built++;
   if (!punit) {
           notify_conn(game.est_connections, city_tile(pcity),
                   E_WONDER_WILL_BE_BUILT, ftc_server,
                   _("Notice: %s in %s creating illegal segfault. Report to admin immediately!"),
                   utype_name_translation(utype), 
                   city_link(pcity));
     return NULL;              // 17Oct2022 line below was segfault:
   }
   saved_unit_id = punit->id;