判断是否为空

if response.result is NSNULL {

}

方法设置默认值

public init(context: MapContext? = nil, shouldIncludeNilValues: Bool = false){
        self.context = context  //默认值 context 为nill
        self.shouldIncludeNilValues = shouldIncludeNilValues  // 默认值 shouldIncludeNilValues 为false
    }


public init(mappingType: MappingType, JSON: [String: Any], toObject: Bool = false, context: MapContext? = nil, shouldIncludeNilValues: Bool = false) {

}

//调用，toObject 省略了
let map = Map(mappingType: .fromJSON, JSON: json, context: context1, shouldIncludeNilValues: shouldIncludeNilValues)