[SWIFT 4 ] generated swift4 models are not building.

I create the swift 4 models but the model is not building in latest Xcode.

my yaml file is attached.

swagger_1.yaml.zip

command to generate the swift4 files

swagger-codegen generate -i swagger_1.yaml -l swift4

generated swift4 models attached below.

Models.zip

I took ONLY the models and put it in my project file. I dont need the rest of the files. My main objective is to generate only model classes.

public func encode(to encoder: Encoder) throws {

    var container = encoder.container(keyedBy: String.self)

    try container.encodeIfPresent(id, forKey: "id")
    try container.encodeIfPresent(username, forKey: "username")
    try container.encodeIfPresent(firstName, forKey: "firstName")
    try container.encodeIfPresent(lastName, forKey: "lastName")
    try container.encodeIfPresent(sex, forKey: "sex")
}

// Decodable protocol methods

public required init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: String.self)

    id = try container.decodeIfPresent(Int64.self, forKey: "id")
    username = try container.decodeIfPresent(String.self, forKey: "username")
    firstName = try container.decodeIfPresent(String.self, forKey: "firstName")
    lastName = try container.decodeIfPresent(String.self, forKey: "lastName")
    sex = try container.decodeIfPresent(Sex.self, forKey: "sex")
}

The models are not building.... lines inside encode and decode "String.self" is not building. .. also explicit encoder and decoders are not required in swift4 unless we have different names in json response..

The error is

In argument type 'String.Type', 'String' does not conform to expected type 'CodingKey'

Reproduce the issue with the attached swagger_1.yaml and the command swagger-codegen generate -i swagger_1.yaml -l swift4. Inspect the generated model files in Models.zip, especially their encode and decode methods, and build them in the reported Xcode setup. Done means the generated models compile without the CodingKey error while remaining usable without the other generated files.