slsm: print empty string if app is NULL

security/slsm/tree.c

@@ -239,7 +239,7 @@ ssize_t slsm_serialize_subtree(struct slsm_str *buf, struct slsm_str *path_buf,
 	for (i = 0; i < t->rules_used; i++) {
 		ret = slsm_str_append(buf, "p=%s%ca=%s%cm=%u%cf=%u%c",
 				path_buf->buf, '\0',
-				t->rules[i].app, '\0',
+				t->rules[i].app ? t->rules[i].app : "", '\0',
 				t->rules[i].perms.mode, '\0',
 				t->rules[i].perms.flags, '\0');
 		if (ret)