diff --git a/apps/wpm/tasks.py b/apps/wpm/tasks.py
index 6dafc52d..9dd6e657 100644
--- a/apps/wpm/tasks.py
+++ b/apps/wpm/tasks.py
@@ -70,7 +70,7 @@ def cal_exp_duration_sec(stlogId: str='', all=False, now: datetime=None):
     if now is None:
         now = timezone.now()
     for stlog in stlogs:
-        if stlog.duration_sec is None and stlog.end_time is not None:
+        if stlog.duration_sec is None and stlog.end_time:
             stlog.duration_sec = (stlog.end_time-stlog.start_time).total_seconds()
             stlog.save()
         is_shutdown_stlog = True