问Angular6 - 'json‘在类型'Object’上不存在

EN

public getList() {
        return this.http.get(environment.serverUrl +'/vmsdata/v1/tftoport/customer/1001')
            .toPromise()
            .then(response => response.json()
            .then(json => {
                console.log('data', json.items);
                return json.items;
            });
    }