diff --git a/app/helper/display.py b/app/helper/display.py
index 705a5bd2..3dd6eb76 100644
--- a/app/helper/display.py
+++ b/app/helper/display.py
@@ -10,6 +10,7 @@ import os
 class DisplayHelper(metaclass=Singleton):
 
     def __init__(self):
+        self._display = None
         if not SystemUtils.is_docker():
             return
         try: