[Swift4] Model type mismatch ( decodeIfPresent)

[riceman2]

Thank you as always.

Description

I generate Sagger Code(Use 2.3.0 and 3.0.0)
Enum is included in the model fails to build.

Like this.

public enum ModelType: String, Codable { 
    case list = "list"
    case map = "map"
    case camera = "camera"
    case setting = "setting"
    case other = "other"
}

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

    type = try container.decodeIfPresent(String.self, forKey: "type")
    ...
}

Error message:
"Cannot assign value of type 'String?' to type 'Button.ModelType?'"

Swagger-codegen version

3.0.0 2.3.0 both latest version.

Swagger declaration file content or url

Command line used for generation

java -jar swagger-codegen-cli-3.0.0-20170924.102354-5.jar generate -i swagger.yaml -l swift4 -o temp/
java -jar swagger-codegen-cli-2.3.0-20171002.073400-174.jar generate -i swagger.yaml -l swift4 -o temp/

Steps to reproduce

run the above command

Related issues/PRs

Suggest a fix/enhancement

I replace the code.
e.g.
type = try container.decodeIfPresent(String.self, forKey: "type")
↓
type = try container.decodeIfPresent(Button.ModelType.self, forKey: "type")

I am happy that it can be done automatically :)

[wing328]

cc @jgavris @ehyche @jaz-ah @Edubits