I can get the attribute 'updateAt from Alartmanager API api/v2/alerts but no this from webhook

question
I can get the attribute 'updateAt from Alartmanager API api/v2/alerts but no this from webhook。
Raw data as below:
json.loads(request.data)
Clould you please share some ideas?

VERSION V0.20.0

json.loads(request.data)

< class 'dict' >: {
	'receiver': 'webhook',
	'status': 'firing',
	'alerts': [{
		'status': 'firing',
		'labels': {
			'Node': 'instance',
			'alertname': '节点状态',
			'instance': 'localhost:9100',
			'job': 'node-export',
			'severity': 'Critical'
		},
		'annotations': {
			'description': '当前服务器可能已经宕机,请及时排查问题',
			'summary': '服务器故障',
			'value': '0'
		},
		'startsAt': '2019-12-17T11:56:20.873303345Z',
		'endsAt': '0001-01-01T00:00:00Z',
		'generatorURL': 'http://prometheus:9090/graph?g0.expr=up%7Bjob%3D%22node-export%22%7D+%3D%3D+0&g0.tab=1',
		'fingerprint': '24eccb8d84d71e24'
	}],
	'groupLabels': {},
	'commonLabels': {
		'Node': 'instance',
		'alertname': '节点状态',
		'instance': 'localhost:9100',
		'job': 'node-export',
		'severity': 'Critical'
	},
	'commonAnnotations': {
		'description': '当前服务器可能已经宕机,请及时排查问题',
		'summary': '服务器故障',
		'value': '0'
	},
	'externalURL': 'http://alertmanager:9093',
	'version': '4',
	'groupKey': '{}:{}'
}

GET http://localhost:9093/api/v2/alerts

"annotations":{
"description": "当前服务器可能已经宕机,请及时排查问题",
"summary": "服务器故障",
"value": "0"
},
"endsAt": "2019-12-17T12:03:05.873Z",
"fingerprint": "24eccb8d84d71e24",
"receivers":[
{
"name": "webhook"
}
],
"startsAt": "2019-12-17T11:56:20.873Z",
"status":{
"inhibitedBy":[],
"silencedBy":[],
"state": "active"
},
"updatedAt": "2019-12-17T12:00:05.875Z",

No source file, test, or entry point is named. Start by comparing the Alertmanager v2 alert response with the webhook payload and the webhook/API documentation; done means establishing whether updatedAt is intentionally absent or defining a documented, tested behavior for it.