Database Error when Searching

[Master Of Unive]

I received an email which notifies me a database error, it is as below

My forum doesn't happen a problem with it, search functions are still working.
Can anyone spot where the problem comes from, and how to reproduce it?

Database error in vBulletin 4.2.2:

Invalid SQL:

SELECT post.*,userfield.*, usertextfield.*, user.*, IF(displaygroupid=0, user.usergroupid, displaygroupid) AS displaygroupid,avatar.avatarpath, NOT ISNULL(customavatar.userid) AS hascustomavatar,
customavatar.dateline AS avatardateline, customavatar.width AS width, customavatar.height AS height,
customavatar.height_thumb AS height_thumb, customavatar.width_thumb AS width_thumb, customavatar.filedata_thumb
FROM post AS post
LEFT JOIN user AS user ON (user.userid = post.userid)
LEFT JOIN userfield AS userfield ON (user.userid = userfield.userid)
LEFT JOIN usertextfield AS usertextfield ON (user.userid = usertextfield.userid)
LEFT JOIN avatar AS avatar ON (avatar.avatarid = user.avatarid)
LEFT JOIN customavatar AS customavatar ON (customavatar.userid = post.userid)
WHERE post.postid IN (.);

MySQL Error : You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')' at line 10
Error Number : 1064
Request Date : Thursday, July 2nd 2015 @ 10:15:46 AM
Error Date : Thursday, July 2nd 2015 @ 10:15:46 AM
Script : http://xxxx.com/forum/search.php?searchid=318478
Referrer : http://xxxx.com/forum/search.php
IP Address : 60.xx.xx.xx
Username : someone
Classname : vB_Database