[PHP] Bug deserialize default responses as a Model

Description

I'm generating clients that make use of default responses for other HTTP codes (implying an error). It's defined as a Model (code, message) in definitions in the swagger file.

...
  responses:
    '200':
      description: pet response
      schema:
        type: array
        items:
          $ref: '#/definitions/Pet'
    default:
      description: error payload
      schema:
        $ref: '#/definitions/ErrorModel'
...

After generating the client API with swagger-codegen, when catching an ApiException, the deserialized response object ApiException::responseObject is empty (it is an an instance of ErrorModel as expected, but with no content).

Swagger-codegen version

2.3.0

Swagger declaration file content or url

gist: minimal swagger.json example

Command line used for generation

java -jar bin/swagger-codegen-cli.jar generate -i swagger.json \
  -l php \
  -o build/ \
  --git-user-id "vendor" \
  --git-repo-id "ws-clients" \
  -DpackagePath=.,srcBasePath=lib,variableNamingConvention=camelCase,invokerPackage="MyCie\\Service",apiTests=false,apiDocs=false,modelTests=false,modelDocs=false

Steps to reproduce

With the generated client:

• try to make a request for a non-existing pet
• Expect $e->getResponseObject() to be a fully hydrated instance of ErrorModel
• Got an empty instance of ErrorModel instead

$petApi = new PetApi();

try {
  $pet = $api->getPetById(123);
  ...
} catch (ApiException $e) {
  $errorModel = $e->getResponseObject();
  print_r($errorModel); // empty ErrorModel
}

Suggest a fix/enhancement

I checked the generated code and the bug seem to be located in the catch part of the {{operationId}}WithHttpInfo methods:

try {
    ...
} catch (ApiException $e) {
    switch ($e->getCode()) {
        case 200:
            $data = ObjectSerializer::deserialize(
                $e->getResponseBody(),
                '\MyCie\Service\Model\Pet',
                $e->getResponseHeaders()
            );
            $e->setResponseObject($data);
            break;
        default:
            $data = ObjectSerializer::deserialize(
                $e->getResponseBody(), // <-- works with json_decode($e->getResponseBody())
                '\MyCie\Service\Model\ErrorModel',
                $e->getResponseHeaders()
            );
            $e->setResponseObject($data);
            break;
    }
    throw $e;
}

We can see that there is a specific test for this in the try part of same function in the api.mustache file, line 164

https://github.com/swagger-api/swagger-codegen/blob/36f69a034d2c6503b3e3cee00d10ab8944cc5be6/modules/swagger-codegen/src/main/resources/php/api.mustache#L163-L166

So a possible fix would be doing something similar when deserializing for ApiException objects.

I can work on a PR for this, as I really need it, but I have no experience with mustache templates and will not be able to test edge cases.

So I would need help for testing my PR.

Start with modules/swagger-codegen/src/main/resources/php/api.mustache, comparing the response deserialization in the try path around line 164 with the ApiException catch path. Reproduce the generated PHP client using the linked minimal swagger.json example and verify that a default error response hydrates ErrorModel in getResponseObject(), including the generated client behavior shown in the issue.