any idea where this SQL query comes from?

Hi,

I'm seeing a new error pop up on my Akonadi terminal:

Error code: 1064
DB error:  "You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '= NULL )' at line 1"
Error text: "You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '= NULL )' at line 1 QMYSQL: Unable to execute query"
Query: "SELECT DISTINCT CollectionTable.id, CollectionTable.parentId FROM CollectionTable LEFT JOIN CollectionMimeTypeRelation ON ( CollectionMimeTypeRelation.Collection_id = CollectionTable.id ) LEFT JOIN MimeTypeTable ON ( CollectionMimeTypeRelation.MimeType_id = MimeTypeTable.id ) WHERE (  = NULL )"
Failed to query search collections 


Any idea where that SELECT DISTINCT query comes from? I can only find one in Kontact's summary plugin, but I'm seeing this error when Kontact isn't even running ...

Thanks,
R.