class ShortURL_Meta { DateTime? validSince; DateTime? validUntil; int? maxVisits; ShortURL_Meta(this.validSince, this.validUntil, this.maxVisits); ShortURL_Meta.fromJson(Map json): validSince = json["validSince"] != null ? DateTime.parse(json["validSince"]) : null, validUntil = json["validUntil"] != null ? DateTime.parse(json["validUntil"]) : null, maxVisits = json["maxVisits"]; }