app.py

@@ -442,12 +442,17 @@ def get_total_expense_for_list(list_id, start_date=None, end_date=None):
     return query.scalar() or 0
 
 
+
 def update_list_categories_from_form(shopping_list, form):
-    category_ids = form.getlist("categories")
+    cat = form.get("categories")
     shopping_list.categories.clear()
-    if category_ids:
-        cats = Category.query.filter(Category.id.in_(category_ids)).all()
-        shopping_list.categories.extend(cats)
+    if cat:
+        try:
+            cid = int(cat)
+            cats = Category.query.filter(Category.id == cid).all()
+            shopping_list.categories.extend(cats)
+        except ValueError:
+            pass
 
 
 def generate_share_token(length=8):