Zend Framework 2: Creating forms from configuration - how to fix ServiceNotCreatedException

I want to create a form in Zend Framework 2 from configuration, similar as described in the docs. So instead of doing this in the form class for every element:

// [...]

$this->add(array(
    'name' => 'fname',
    'type' => 'text',     
));

// [...]v

I want to do it like this:

// [...]

$form = $factory->createForm(array(
    'elements' => array(
        array(
            'spec' => array(
                'name' => 'fname',
                'type' => 'text',
            ),
        ),
    ),
));

// [...]

Since I am new to the framework, I am still a bit unsure as where things go & what is the correct way to do things, but I think I am on a good track – I just need to get things working to understand them more.

Currently my code results in an exception which leaves me a bit puzzled, although I understand it somehow:

An exception was raised while creating "MyForm"; no instance returned

Besides my confusion, I already have an idea where my code might go wrong.

The form class looks pretty simple because the actual elements won't be injected here:

namespace My\Form;

use Zend\Form\Form;

class MyForm extends Form
{
    public function __construct()
    {
        parent::__construct();

        $this->setAttribute('method', 'post');
        $this->setAttribute('action', '/some-action');
    }
}

The configuration for the form elements looks like this:

namespace My\Form;

use Zend\Form\Factory;

class MyFormFactory extends Factory
{
    public function __construct()
    {
        $factory = new Factory();

        $form = $factory->createForm(array(
            'elements' => array(
                array(
                    'spec' => array(
                        'name' => 'fname',
                        'type' => 'text',
                    ),
                ),
            ),
        ));

        return $form;
    }
}

To wire the two together, I have this service manager configuration in the module's module.config.php:

'service_manager' => array(
    'factories' => array(
        'MyForm' => function ($servicemanager) {
            $form = new \My\Form\MyForm();
            $factory = $servicemanager->get('MyFormFactory');
            $form->add($factory);
            return $form;
        },
        'MyFormFactory' => function ($servicemanager) {
            $factory = new \My\Form\MyFormFactory();
            return $factory;
        },
    ),
),

And last but not least, the controller:

 namespace My\Controller;


use Zend\Mvc\Controller\AbstractActionController;
use Zend\View\Model\ViewModel;

class MyController extends AbstractActionController
{
    public function indexAction()
    {
        $form = $this->getServiceLocator()->get('MyForm');

        return new ViewModel(array(
            'form' => $form,
        ));
    }
}

As already said, the only thing that happens is the exception which is actually pretty clear: The MyForm class does not return an instance. To fix this, I already tried to return something, but that did not do anything.

What needs to be changed to get the form created? Is my approach any good or am I on the wrong track?