update: fix coupon multi generate

app/Http/Controllers/Admin/CouponController.php

@@ -90,8 +90,8 @@ class CouponController extends Controller
         DB::beginTransaction();
         if (!Coupon::insert(array_map(function ($item) use ($coupon) {
             // format data
-            $item['limit_plan_ids'] = json_encode($coupon['limit_plan_ids']);
-            $item['limit_period'] = json_encode($coupon['limit_period']);
+            if (is_array($item['limit_plan_ids'])) $item['limit_plan_ids'] = json_encode($coupon['limit_plan_ids']);
+            if (is_array($item['limit_period'])) $item['limit_period'] = json_encode($coupon['limit_period']);
             return $item;
         }, $coupons))) {
             DB::rollBack();