PHPStan warning: using nullsafe method call on non-nullable type

Problem/Motivation

PHPStan (level 5) reports an error in src/Controller/CollectionExportController.php:

------ ----------------------------------------------------------------------------------------------------
 Line   src/Controller/CollectionExportController.php
------ ----------------------------------------------------------------------------------------------------
 68     Using nullsafe method call on non-nullable type Drupal\search_api\ServerInterface. Use -> instead.
        nullsafe.neverNull
------ ----------------------------------------------------------------------------------------------------

In __invoke(), the server instance is fetched and then its backend is checked with an instanceof guard that throws when it is not the Typesense backend. Because a null server would yield a null backend (which is not an instance of SearchApiTypesenseBackend and therefore throws), PHPStan narrows $search_api_server to a non-nullable ServerInterface from that point on. The nullsafe operator on line 68 is consequently redundant, and PHPStan fails the build.

Steps to reproduce

Run static analysis on the module:

ddev phpstan src

Proposed resolution

Drop the nullsafe operator on line 68.