Fatal error: Call to a member function isNew() on a non-object in EmbeddedGroup.php

[catasoft]

Hello

I'm trying to do an update of complex documents in Mandango, documents containing a few embeddeds.

So I get my data from the form as a hierarchical array (custom widgets are used).

So I do a simple: 

$row = $this->getModel()

   ->createQuery(array('_id' => new \MongoId($values['_id'])))

   ->fields(array('_id' => true))

   ->one();

$row->fromArray($values)

Error: Fatal error: Call to a member function isNew() on a non-object in [...]lib\Mandango\src\Mandango\Group\EmbeddedGroup.php on line 98

Please help, I have no idea why this isn't working.

Thank you in advance.