/* It's perfectly valid for a message to have no In-Reply-To
* header. For these cases, we return an empty string. */
/* It's perfectly valid for a message to have no In-Reply-To
* header. For these cases, we return an empty string. */
if (i == message->doc.termlist_end () || id[0] != *prefix)
INTERNAL_ERROR ("Message with document ID of %d has no thread ID.\n",
if (i == message->doc.termlist_end () || id[0] != *prefix)
INTERNAL_ERROR ("Message with document ID of %d has no thread ID.\n",