* Returns a newly talloc'ed string belonging to 'ctx'.
*
* Returns NULL if there is any error parsing the message-id. */
-char *
+static char *
_parse_message_id (void *ctx, const char *message_id, const char **next)
{
const char *s, *end;
/* Carefully avoid adding any self-referential in-reply-to term. */
in_reply_to_message_id = _parse_message_id (message, in_reply_to, NULL);
- if (strcmp (in_reply_to_message_id,
+ if (in_reply_to_message_id &&
+ strcmp (in_reply_to_message_id,
notmuch_message_get_message_id (message)))
{
_notmuch_message_add_term (message, "replyto",