* notmuch_message_destroy on 'message' or until a query from which it
* derived is destroyed).
*
- * This function will not return NULL since Notmuch ensures that every
- * message belongs to a single thread.
+ * This function will return NULL if triggers an unhandled Xapian
+ * exception.
*/
const char *
notmuch_message_get_thread_id (notmuch_message_t *message);