[Swift4] 204 No Content returns error

[nfortenberry]

Description

Swift 4 code-gen issue:
If a request returns a status code of 204 with no content, the completion handler will return an error and nil response. Since a 204 with no content is expected, no error should be thrown.

Swagger-codegen version

Swagger version 2.3.1

Steps to reproduce

In swagger, create a request that returns a 204 and no content.

Suggest a fix/enhancement

An error should not be thrown.

[d-date]

@wing328 Do you know we have 204 response api definition in petstore.yaml? I also need to use 204 response api. If not, we should add as reference.

[d-date]

@nfortenberry By this PR, we can accept no content as Void response.

[nfortenberry]

Great! Thank you!