Fix ValueError when interacting with timeslots

program/views.py

 import json
+import logging
 from datetime import date, datetime, time, timedelta
 
 from django.contrib.auth.models import User
@@ -511,9 +512,9 @@ class APITimeSlotViewSet(viewsets.ModelViewSet):
         start = datetime.combine(date.today(), time(0, 0))
         end = start + timedelta(days=60)
 
-        if (start := self.request.query_params.get('start')) and (end := self.request.query_params.get('end')):
-            start = datetime.combine(datetime.strptime(start, '%Y-%m-%d').date(), time(0, 0))
-            end = datetime.combine(datetime.strptime(end, '%Y-%m-%d').date(), time(23, 59))
+        if ('start' in self.request.query_params) and ('end' in self.request.query_params):
+            start = datetime.combine(datetime.strptime(self.request.query_params.get('start'), '%Y-%m-%d').date(), time(0, 0))
+            end = datetime.combine(datetime.strptime(self.request.query_params.get('end'), '%Y-%m-%d').date(), time(23, 59))
 
         # Endpoints
 
@@ -523,6 +524,7 @@ class APITimeSlotViewSet(viewsets.ModelViewSet):
         #     Returns timeslots of the given show and schedule
         #
         if show_pk and schedule_pk:
+            logging.error('############################################# {} {}'.format(start, end))
             return TimeSlot.objects.filter(show=show_pk, schedule=schedule_pk, start__gte=start, end__lte=end).order_by('start')
 
         #