Ok, how about a message that communicates a few key things - there is no search_query, it was created with an older version of chef-vault, and an update command will store the search_query for future use.  So something like:

#{vault}/#{item} does not have a stored search_query, probably because it was created with an older version of chef-vault. Use the 'knife vault update' command to update the databag with the search string.