Outdated configuration can throw fatal error

Problem/Motivation

This code's method for loading configuration has the same potential for failure as documented in https://www.drupal.org/project/drupal/issues/3512487 🐛 Error: Call to a member function getConfigDependencyName() on null Active

Steps to reproduce

1. A site entity has configuration that, for whatever reason, is now outdated with the configuration schema of the entity.
2. Executing drush content_entity_sync:export node will result in a fatal error, with Call to a member function getConfigDependencyName() on null in Drupal\content_entity_sync\Services\ContentEntitySerializer->serialize() (line 47

Proposed resolution

While the obvious solution is to put the burden on the developer working with the site to clean up the outdated configuration, this module could easily add a check that would avoid the problem in the first place, by checking for the ability to use getConfigDependencyName() before calling it.

Remaining tasks

Provide a merge request.

User interface changes

N/A

API changes

N/A

Data model changes