OrderChangeManager: Prevent creation of 0 € invoices

src/pretix/base/services/orders.py

@@ -1725,7 +1725,8 @@ class OrderChangeManager:
         i = self.order.invoices.filter(is_cancellation=False).last()
         if self.reissue_invoice and i and self._invoice_dirty:
             self._invoices.append(generate_cancellation(i))
-            self._invoices.append(generate_invoice(self.order))
+            if invoice_qualified(self.order):
+                self._invoices.append(generate_invoice(self.order))
 
     def _check_complete_cancel(self):
         current = self.order.positions.count()

src/tests/base/test_orders.py

@@ -1393,6 +1393,15 @@ class OrderChangeManagerTests(TestCase):
         self.ocm.commit()
         assert self.order.invoices.count() == 3
 
+    @classscope(attr='o')
+    def test_no_new_invoice_for_free_order(self):
+        generate_invoice(self.order)
+        assert self.order.invoices.count() == 1
+        self.ocm.change_price(self.op1, Decimal('0.00'))
+        self.ocm.change_price(self.op2, Decimal('0.00'))
+        self.ocm.commit()
+        assert self.order.invoices.count() == 2
+
     @classscope(attr='o')
     def test_reissue_invoice_disabled(self):
         self.ocm.reissue_invoice = False