fix(ruby-core-lib): fix returning nil instead of empty request params

[MaryamAdnan3]

What

Fix returning nil instead of empty request params

Why

This behavior causes Faraday urlEncode middleware to assign content-type to x-www-form-urlencoded.

closes #20

Type of change

Select multiple if applicable.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause a breaking change)
• Tests (adds or updates tests)
• Documentation (adds or updates documentation)
• Refactor (style improvements, performance improvements, code refactoring)
• Revert (reverts a commit)
• CI/Build (adds or updates a script, change in external dependencies)

Dependency Change

If a new dependency is being added, please ensure that it adheres to the following guideline https://github.com/apimatic/apimatic-codegen/wiki/Policy-of-adding-new-dependencies-in-the-core-libraries

Breaking change

If the PR is introducing a breaking change, please ensure that it adheres to the following guideline https://github.com/apimatic/apimatic-codegen/wiki/Guidelines-for-maintaining-core-libraries

Testing

List the steps that were taken to test the changes

Checklist

• My code follows the coding conventions
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added new unit tests

[sufyankhanrao]

LGTM