[BUG][Golang][client] README.md example wrong return value

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

All my operations are generated with a return signature that is a 3-tuple, for example:

func (a *UserApiService) Create(ctx context.Context, userCreatePayload UserCreatePayload) (UserCreateResponse, *http.Response, error) {

README.md however lists this as an example:

r, err := client.Service.Operation(auth, args)

This is wrong as it suggests that the return value is a 2-tuple.

openapi-generator version

Happens both in 4.0.0-beta3 and 3.3.4

OpenAPI declaration file content or url

I'm honestly not sure how to find a reproducer for this. It happens with openapi-generator installed through npm, but I can't reproduce it on the petstore example, where the generated operations really do seem to return 2-tuples.

The template go/api.mustache does have this:

func (a *{{{classname}}}Service) {{{nickname}}}(ctx context.Context{{#hasParams}}, {{/hasParams}}{{#allParams}}{{#required}}{{paramName}} {{{dataType}}}{{#hasMore}}, {{/hasMore}}{{/required}}{{/allParams}}{{#hasOptionalParams}}localVarOptionals *{{{nickname}}}Opts{{/hasOptionalParams}}) ({{#returnType}}{{{returnType}}}, {{/returnType}}*http.Response, error) {

which suggests that the first return value only gets rendered if {{returnType}} is defined, but the README doesn't take this into account. However I'm not sure where this value comes from and why I can't reproduce on the petstore example.

Command line used for generation

openapi-generator generate -g go -c config/languages/go.json -i spec/full_spec.yaml -o generated/myclient

Steps to reproduce

For me, the reproducer is just running the above command.

Related issues/PRs

I haven't found any.

Suggest a fix

I think that taking the {{returnValue}} variable into account in the README example should fix this.

Read the Go client example in README.md and compare its return-value usage with the signature rendered by go/api.mustache. Confirm how the return value is represented for generated operations, then update the README example so it matches the documented generated signature and verify the example is consistent with the template.