Fix VKey reconstruction issue in BillingEvent (#805)

* Fix VKey reconstruction issue in BillingEvent

* Rebase on head

db/src/main/resources/sql/flyway/V58__drop_default_value_and_sequences_for_billing_event.sql

@@ -0,0 +1,21 @@
+-- Copyright 2020 The Nomulus Authors. All Rights Reserved.
+--
+-- Licensed under the Apache License, Version 2.0 (the "License");
+-- you may not use this file except in compliance with the License.
+-- You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+
+alter table "BillingCancellation" alter column billing_cancellation_id drop default;
+alter table "BillingEvent" alter column billing_event_id drop default;
+alter table "BillingRecurrence" alter column billing_recurrence_id drop default;
+
+drop sequence "BillingCancellation_billing_cancellation_id_seq";
+drop sequence "BillingEvent_billing_event_id_seq";
+drop sequence "BillingRecurrence_billing_recurrence_id_seq";