Plugin errors at ShippingService->getLabel() is null. [#3135383]

I ran into an issue where I couldn't activate the plugin in the Shipping Method form.

The following error would be logged, and the plugin form would not load:

Ein AJAX-HTTP-Error occured.
HTTP-Code: 200
Path: /admin/commerce/config/shipping-methods/add?ajax_form=1
Status: OK
Response: TypeError: Return value of Drupal\commerce_shipping\ShippingService::getLabel() must be of the type string, null returned in Drupal\commerce_shipping\ShippingService-&gt;getLabel() (line 54 of /Users/xx/xx/xx/xx/modules/contrib/commerce_shipping/src/ShippingService.php)."

I compared the FlatRate class of the Commerce_Shipping plugin to the ShippingByWeight class and noticed that the 'rate_label' in defaultConfiguration() was set to NULL instead of an empty string as in the FlatRate class.
Changing the default to an empty string fixed the error response.

Attached is the Patch in question.

Cheers!