getMenuLinkNodeAttached parameter entity check

Hi,

I am using the module in combination with a couple of other modules and faced the following issue.

I am using https://www.drupal.org/project/multiple_registration to generate role based registration pages
This module allows defining custom URL for the registration forms.
In my use case, I defined a URL: /user/register/from

When trying to add this URL to a menu path, there is error being generated by function getMenuLinkNodeAttached in the class ContentEntityNormalizer. After debugging it, I realized that the function assumes that the last parameter of the URL is an entity ID (which is not the case) and tries to load it.

The patch will arrive in a couple of minutes