Avoid raising exception on format_duration(None)

Fixes #25

Dockerfile

@@ -6,7 +6,7 @@ RUN npm install && \
 
 FROM python:3.10.9-alpine
 
-ENV VERSION_NUMBER 0.1.2-5-g33e136a
+ENV VERSION_NUMBER 0.1.2-6-g751182d
 ENV PROD 1
 
 RUN apk add \

src/web/common/util/time.py

@@ -9,7 +9,7 @@ def now() -> datetime:
 
 
 def format_duration(
-    duration: timedelta, format_string: str = "%H hours %m minutes"
+    duration: timedelta | None, format_string: str = "%H hours %m minutes"
 ) -> str:
     """
     Format timedelta into the specified format_string.
@@ -23,6 +23,9 @@ def format_duration(
     hour_seconds = 60 * minute_seconds
     day_seconds = 24 * hour_seconds
     if not isinstance(duration, timedelta):
+        if duration == None:
+            duration = timedelta(seconds=0)
+        else:
             duration = timedelta(seconds=duration)
     seconds_total = int(duration.total_seconds())
     # timestamps where end is before start

tests/test_time.py

@@ -56,3 +56,9 @@ class FormatDurationTest(unittest.TestCase):
         delta = timedelta(hours=-2)
         result = format_duration(delta, "%H hours")
         self.assertEqual(result, "0 hours")
+
+    def test_none(self):
+        try:
+            format_duration(None)
+        except TypeError as exc:
+            assert False, f"format_duration(None) raised an exception {exc}"