Fix null command references (in service commands list) during Drupal …

…bootstrap phase (which causes "PHP Fatal error: Cannot redeclare drupal_error_levels() (previously declared in..." in test_81_drupal10_highest CI pipeline)

src/Command/ServiceCommandlist.php

@@ -17,6 +17,6 @@ public function addCommandReference($command): void
 
     public function getCommandList(): array
     {
-        return $this->commandList;
+        return array_filter($this->commandList);
     }
 }