Fix parameters with schema reference

[sergiopatricio]

Problem

Reading https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md#parameterObject it says that schema can be a "Schema Object" or a "Reference Object".

I think the code on rswag/specs/request_factory.rb is not prepared for the "Reference Object" option. When schema has a $ref and not a type it raises an exception:

NoMethodError:
   undefined method `to_sym' for nil:NilClass

             case param[:schema][:type].to_sym
                                       ^^^^^^^

Solution

Don't raise an exception, and instead add a fallback as we had before version 2.6.0.

This concerns this parts of the Open API Specification:

• Parameter Object

The changes I made are compatible with:

• OAS2
• OAS3
• OAS3.1

Related Issues

#563

Checklist

• Added tests
• Changelog updated
• Added documentation to README.md

Steps to Test or Reproduce

Outline the steps to test or reproduce the PR here.