according to the doc, this should say `content` as it will use the mapping of the field to know the phpcr name: 
http://docs.doctrine-project.org/projects/doctrine-phpcr-odm/en/latest/reference/association-mapping.html#referrers-to-inverse-the-reference-relation

i hope after your fixes this will actually work, but best verify if it does.

you also need to change the MenuNode namespace now that we moved to the model.