diff --git a/lib/Service/Importer/BoardImportService.php b/lib/Service/Importer/BoardImportService.php
index 657f938b2..ee1ff7dc7 100644
--- a/lib/Service/Importer/BoardImportService.php
+++ b/lib/Service/Importer/BoardImportService.php
@@ -61,7 +61,7 @@ class BoardImportService {
 	private ICommentsManager $commentsManager;
 	private IEventDispatcher $eventDispatcher;
 	private string $system = '';
-	private ?ABoardImportService $systemInstance;
+	private ?ABoardImportService $systemInstance = null;
 	private array $allowedSystems = [];
 	/**
 	 * Data object created from config JSON