This is the line which makes it all work. In order for EntityMultiCheckbox, EntityRadio & EntitySelect to work they required access to the EntityManager so they can fetch the options from the database, this is provided by an option called `object_manager` (see \DoctrineModule\Form\Element\Proxy). Here I am setting that option.

It saves having to call

`$form->get('element_name')->setOptions(array('object_manager', $entityManager);`

after the form has been created.