struct Landmark: Codable {
    var name: String
    var age: Int
    var isCommander: Bool
    
    enum CodingKeys: String, CodingKey {
        case name = "__name"
        case age = "age"
        case isCommander = "isCommander"
    }
}


let landmarkStr = """
{
    "__name" : "Hello",
    "age" : 18,
    "isCommander" : null
}
"""

let jsonDecoder = FaultToleranceJSONDecoder()
let model = try! jsonDecoder.decode(String.self, from: landmarkStr.data(using: .utf8)!)
print(model)