Symfony Container not available for Legacy Environment

The PrestaShop Module Services documentation mentions that we are able to obtain the Symfony Container from our modules. This isn't working for me when extending PaymentModule on 1.7.5.2.

public function getContent()
{
    // Error: Attempted to call an undefined method named "getContainer" of class "AdminModulesController".
    $formFactory = $this->context->controller->getContainer()->get('form.factory');
}

I did find something similar in the Psaddonsconnect which does work for me. Should we use this instead?

public function getContent()
{
    global $kernel;
    $formFactory = $kernel->getContainer()->get('form.factory');
}

Start with the linked Services documentation and compare its container-access example with the legacy PaymentModule/AdminModulesController context described here. Verify which approach is supported for PrestaShop 1.7.5.2, then update the documentation to state the correct version-specific usage and any relevant limitations.