pod 'HandyJSON', '~> 5.0.1'

struct UserInfoModel: HandyJSON {
var avatar: String!
var nick: String!
var username: String!
}
//主要问题在这里instance对应上面结构题的属性成了可选的
` static func _transform(dict: [String: Any]) -> _ExtendCustomModelType? {

var instance: Self
    if let _nsType = Self.self as? NSObject.Type {
        instance = _nsType.createInstance() as! Self
    } else {
        instance = Self.init()
    }
    instance.willStartMapping()
    _transform(dict: dict, to: &instance)
    instance.didFinishMapping()
    return instance
}`