[TYPO3-mvc] Check for empty object storage in Query

[Alex Bailey]

Hi,
I'm building a query which goes somewhat like this:

If the object storage is empty OR the object storage is not empty but 
contains X objects

the second part is no problem, concanating the querys together so I can 
check if certain objects exist in the storage but I can't seem to get 
that first check working to find out if the storage is empty altogether.

I tried:

$query->equals('allowedUsergroups',0)
$query->equals('allowedUsergroups',NULL)
$query->equals('allowedUsergroups',false)

but none seem to do the trick.

Am I missing something?

regards

Alex