Update lightrag_manager.py

lightrag_manager.py

@@ -661,7 +661,7 @@ class PersistentLightRAGManager:
                                 file_type, file_size, blob_url, content_text, 
                                 processing_status, created_at, updated_at
                             ) VALUES (
-                                gen_random_uuid(), 'system', $1::uuid, 'lightrag_storage.json', 
+                                gen_random_uuid(), NULL, $1::uuid, 'lightrag_storage.json', 
                                 'LightRAG Storage Data', 'json', $2, 'database://storage', $3, 
                                 'processed', NOW(), NOW()
                             )