Factory not being found by FormElementManager

error

Catchable fatal error: Argument 1 passed to Ticker\Form\TickerFieldset::__construct() 
must implement interface Zend\Stdlib\Hydrator\HydratorInterface, none given, called in 
../vendor/zendframework/zend-form/src/FormElementManager.php on line 174 
and defined in /Ticker/Form/TickerFieldset.php on line 11

module.config.php

<?php

return array(
    'service_manager' => [
        'invokables' => [
            'Ticker\Form\Form'               => 'Ticker\Form\Form',
            'Ticker\Hydrator\TickerHydrator' => 'Ticker\Hydrator\TickerHydrator',
        ],
        'factories'  => [
            'Ticker\Table\TickerTable'     => 'Ticker\Table\Factory\TickerTableFactory',
            'Ticker\Service\TickerService' => 'Ticker\Service\Factory\TickerServiceFactory',
        ],
    ],
    'form_elements'   => [
        'factories' => [
            'Ticker\Form\TickerFieldset' => 'Ticker\Form\Factory\TickerFieldsetFactory',
        ]
    ],
    'view_manager'    => [
        'template_map' => [
            'ticker/admin/index' => __DIR__ . '/../view/ticker/admin/index.phtml',
            'ticker/admin/add'   => __DIR__ . '/../view/ticker/admin/add.phtml',
        ]
    ],
    'view_helpers'    => [
        'invokables' => [
            'tickerMenu' => 'Ticker\View\Helper\TickerMenu',
        ]
    ],
    'router'          => [
        'routes' => [
            'zfcadmin' => [
                'child_routes' => [
                    'ticker' => [
                        'type'          => 'literal',
                        'options'       => [
                            'route'    => '/ticker',
                            'defaults' => [
                                'controller' => 'Ticker\Controller\Admin',
                                'action'     => 'index'
                            ]
                        ],
                        'may_terminate' => true,
                        'child_routes'  => [
                            'add' => [
                                'type'    => 'literal',
                                'options' => [
                                    'route'    => '/add',
                                    'defaults' => [
                                        'controller' => 'Ticker\Controller\Admin',
                                        'action'     => 'add',
                                    ]
                                ]
                            ]
                        ]
                    ]
                ]
            ]
        ]
    ],
    'controllers'     => [
        'factories' => [
            'Ticker\Controller\Admin' => 'Ticker\Controller\Factory\Admin',
        ]
    ],
    'navigation'      => [
        'admin'       => [
            'ticker' => [
                'label' => 'Tickers',
                'route' => 'zfcadmin/ticker'
            ]
        ],
        'tickeradmin' => [
            'list' => [
                'label' => 'List Tickers',
                'route' => 'zfcadmin/ticker',
            ],
            'add'  => [
                'label' => 'Add/Edit Ticker',
                'route' => 'zfcadmin/ticker/add',
            ]
        ]
    ]
);

Ticker\Form\Factory\TickerFieldsetFactory.php

<?php

namespace Ticker\Form\Factory;

use Ticker\Form\TickerFieldset;
use Zend\ServiceManager\ServiceLocatorInterface;

// lives in FormElementManager
class TickerFieldsetFactory
{

    public function __invoke(ServiceLocatorInterface $sm)
    {
        die('Reading TickerFieldsetFactory now');
        $hydrator = $sm->getServiceLocator()->get('Ticker\Hydrator\TickerHydrator');
        return new TickerFieldset($hydrator);
    }

}

Ticker\Form\Form.php

<?php

namespace Ticker\Form;

use Zend\Form\Form as BaseForm;

class Form extends BaseForm
{

    public function __construct($name = 'ticker-form', $options = ['method' => 'POST'])
    {
        parent::__construct($name, $options);

        $this->add([
            'type' => 'Ticker\Form\TickerFieldset', // <--
        ]);

        $this->add([
            'name'       => 'save',
            'type'       => 'submit',
            'attributes' => [
                'value' => 'Save',
            ]
        ]);
    }

}