Changes to List schedules entities

the response property _status/messages/items/data became nullable for the status 400

the response property _status/messages/items/detail became nullable for the status 400

the response property links/next became nullable for the status 200

the response property schedules/items/admin_key became nullable for the status 200

the response property schedules/items/creator_account_id became nullable for the status 200

the response property schedules/items/executed_timestamp became nullable for the status 200

the response property schedules/items/expiration_time became nullable for the status 200

the response property schedules/items/payer_account_id became nullable for the status 200

the response property schedules/items/schedule_id became nullable for the status 200