From c6bb60bbbbabc519ee2015a8ebeb6bbe2fba9732 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Luk=C3=A1=C5=A1=20Kucharczyk?= <lukas@kucharczyk.xyz>
Date: Tue, 3 Jan 2023 20:23:49 +0100
Subject: [PATCH] Prevent error from empty timestamps

---
 src/web/tracker/models.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/web/tracker/models.py b/src/web/tracker/models.py
index 30f9811..06da9b9 100644
--- a/src/web/tracker/models.py
+++ b/src/web/tracker/models.py
@@ -41,7 +41,10 @@ class Session(models.Model):
         return f"{str(self.purchase)} {str(self.timestamp_start.date())} ({self.total_duration()}{mark})"
 
     def calculated_duration(self):
-        return self.timestamp_end - self.timestamp_start
+        if self.timestamp_end == None or self.timestamp_start == None:
+            return 0
+        else:
+            return self.timestamp_end - self.timestamp_start
 
     def total_duration(self):
         return (