+ o = parse_object(sha1);
+ if (!o) {
+ error("Trying to write ref %s with nonexistant object %s",
+ lock->ref_name, sha1_to_hex(sha1));
+ unlock_ref(lock);
+ return -1;
+ }
+ if (o->type != OBJ_COMMIT && is_branch(lock->ref_name)) {
+ error("Trying to write non-commit object %s to branch %s",
+ sha1_to_hex(sha1), lock->ref_name);
+ unlock_ref(lock);
+ return -1;
+ }