Fix case when deleting payment/invoice not associated to a member

coin/billing/models.py

@@ -619,6 +619,9 @@ def payment_deleted(sender, instance, **kwargs):
 
     member = instance.member
 
+    if member is None:
+        return
+
     this_member_invoices = [i for i in member.invoices.filter(validated=True).order_by("date")]
     this_member_payments = [p for p in member.payments.order_by("date")]