[FLOW3-general] Repository Query with isEmpty

[flow3 at leakx.net]

Hello.

That is my method:

public function findAllWithoutCategory() {
	$query = $this->createQuery();
	return $query->matching($query->isEmpty('category'))
		->setOrderings(array('name' => 
\TYPO3\FLOW3\Persistence\QueryInterface::
		ORDER_ASCENDING))
		->execute();
}

I want to fetch all rows who has an empty entry in the column 
`category`.

What is wrong ?