Attempting to delete a relationship with a membership type fatals

I hit this in the test suite - it gets upset because it's trying to treat a string field as an integer

// set all membership_type to null
$query = "
UPDATE civicrm_membership_type
SET relationship_type_id = NULL
WHERE relationship_type_id = %1
";

$params = array(1 => array($relationshipTypeId, 'Integer');

NB - the presence of the custom separated string caused a fatal to trigger