Superfish block does not ask for Menu Name

I have installed Superfish and overcome all the problems with library location by moving my library to sites/all/libraries

I also had to make a small change to Drupal\superfish\Plugin\Block as follows:

*   deriver = "Drupal\system\Plugin\Derivative\SystemMenuBlock"

Change to

*   derivative = "Drupal\system\Plugin\Derivative\SystemMenuBlock"

So, I finally get a block to configure and there is no field for the menu name. I see that it is attempted in the block code thus:

$menu_name = $this->getDerivativeId();

The problem is that I haven't actually told this block I want to use the Main Menu and so understandably when I enable and go to my site I get WSOD with this underlying error:

LogicException: No menu name provided for menu.active_trails cache context. in Drupal\Core\Cache\Context\MenuActiveTrailsCacheContext->getCacheableMetadata() (line 41 of core/lib/Drupal/Core/Cache/Context/MenuActiveTrailsCacheContext.php).

I see that plenty of other people have tried this module and it seems to work for them. I'm using Drupal Core 8.1.6. I have tried this with the latest Superfish dev release and with the current recommended release, and the problem is the same.

Thanks!