fix: Coerce None to zero for missing values

Necessary to handle the case where balance statements are requested on a date when no members have any balance.

itkufs/reports/views.py

@@ -6,6 +6,7 @@
 from django.contrib.auth.decorators import login_required
 from django.db import transaction as db_transaction
 from django.db.models import Q, Sum, Case, When
+from django.db.models.functions import Coalesce
 from django.forms.models import inlineformset_factory, model_to_dict
 from django.http import Http404, HttpResponseRedirect, HttpResponse, HttpRequest
 from django.shortcuts import render
@@ -334,15 +335,21 @@ def balance(request: HttpRequest, group: Group, is_admin=False):
         .filter(filters)
         .filter(group_account=False)
         .aggregate(
-            positive_sum=Sum(
-                Case(
-                    When(normal_balance__gt=0, then="normal_balance"), default=0
-                )
+            positive_sum=Coalesce(
+                Sum(
+                    Case(
+                        When(normal_balance__gt=0, then="normal_balance"),
+                    )
+                ),
+                0,
             ),
-            negative_sum=Sum(
-                Case(
-                    When(normal_balance__lt=0, then="normal_balance"), default=0
-                )
+            negative_sum=Coalesce(
+                Sum(
+                    Case(
+                        When(normal_balance__lt=0, then="normal_balance"),
+                    )
+                ),
+                0,
             ),
         )
     )