FIX: Can't properly filter by nullable primitive datatypes

[CesarD]

Description

Fixed #39 by adding validations that include nullable types and also evaluates the underlying type of an eventually nullable value.
It also fixes another scenario where when comparing non-nullable types against a null value it threw an exception.

Related Issue

Fixes #39

Motivation and Context

Fixes a reported bug.

How Has This Been Tested?

Tested different scenarios via Postman directly against the API.

Screenshots (if appropriate):

N/A

Types of changes

• 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 existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[CesarD]

@matthewtoghill please have a look at this PR you too if you like 😉

[Gonzo345]

Thank you so much to @matthewtoghill and @CesarD for this! （づ￣3￣）づ╭❤️～