diff --git a/app/Http/Controllers/DeviceController.php b/app/Http/Controllers/DeviceController.php
index 08ddbc0..633c910 100644
--- a/app/Http/Controllers/DeviceController.php
+++ b/app/Http/Controllers/DeviceController.php
@@ -219,7 +219,7 @@ class DeviceController extends Controller
                         if (isset($_dataList[$_key])) {
                             $data[$device->monitoring_point][$_key] = $_dataList[$_key][$deviceColumn] ?? null;
                         }else{
-                            $data[$device->monitoring_point][$_key] = $data[$device->monitoring_point][now()->subHours($i+1)->format('Y-m-d H').':00:00'];
+                            $data[$device->monitoring_point][$_key] = $data[$device->monitoring_point][now()->subHours($i+1)->format('Y-m-d H').':00:00'] ?? null;
                         }
                     }
                 }