fix bug in sorting when item type is null

main.py

@@ -31,7 +31,7 @@ def _set_sqlite_pragma(conn, _):
 @app.get("/api/items", response_model=dict[str, Item])
 async def list_items(db: Session = Depends(get_db)):
     # sort by type, id (natural)
-    natsort = lambda s: (s.type, [int(t) if t.isdigit() else t.lower() for t in re.split('(\d+)', s.id)])
+    natsort = lambda s: (s.type or '', [int(t) if t.isdigit() else t.lower() for t in re.split('(\d+)', s.id)])
     items = crud.get_items(db)
     items = sorted(items, key=natsort)
     return {i.id:i for i in items}