加入购物车判断是否返回shoppingkey

@@ -134,7 +134,13 @@ exports.addToCart = (req, res, next) => {
         shoppingKey: req.cookies._SPK || null,
         uid: req.user.uid
     }).then((result) => {
-        res.cookie('_SPK', result.data.shopping_key, {maxAge: 1000 * 60 * 60 * 24 * 365, httpOnly: true, path: '/'});
+        if (result.data && result.data.shopping_key) {
+            res.cookie(
+                '_SPK',
+                result.data.shopping_key,
+                {maxAge: 1000 * 60 * 60 * 24 * 365, httpOnly: true, path: '/'}
+            );
+        }
         res.json(result);
     }).catch(next);
 };