Fatal Error: Call to getEntityTypeId() on null in LinkExtractorService->saveLink()

Problem/Motivation

The linkchecker module is throwing a fatal PHP error when attempting to save links during the link extraction process. The error occurs in the LinkExtractorService::saveLink() method at line 376, where the code attempts to call getEntityTypeId() on a null object.
Error: Call to a member function getEntityTypeId() on null in Drupal\linkchecker\LinkExtractorService->saveLink() (line 376 of /var/lib/tugboat/web/modules/contrib/linkchecker/src/LinkExtractorService.php)
This error prevents the link checking functionality from working properly and can cause site crashes or incomplete link extraction processes.

Steps to reproduce

1. Enable the linkchecker module
2. Configure link checking for content entities
3. Create or update content that contains links
4. Trigger the link extraction process (either manually or via cron)
5. Observe the fatal error in logs

Proposed resolution

The error suggests that an entity object is expected but null is being passed instead. The fix should include:

1. Validate entity states: Ensure entities are properly loaded and accessible before processing
2. Add null checks: Verify that the entity object exists before calling methods on it

Remaining tasks

User interface changes

API changes

Data model changes