fix(spec): ignore empty string for multi-value parameter

[jux61]

Description

Modify function used to get parameter values in plugin spec selector to ignore empty string when parameter is an array

Motivation and Context

Proposal to fix issue #9266, #5176

How Has This Been Tested?

Extend unit test

Screenshots (if appropriate):

Checklist

My PR contains...

• No code changes (src/ is unmodified: changes to documentation, CI, metadata, etc.)
• Dependency changes (any modification to dependencies in package.json)
• Bug fixes (non-breaking change which fixes an issue)
• Improvements (misc. changes to existing features)
• Features (non-breaking change which adds functionality)

My changes...

• are breaking changes to a public API (config options, System API, major UI change, etc).
• are breaking changes to a private API (Redux, component props, utility functions, etc.).
• are breaking changes to a developer API (npm script behavior changes, new dev system dependencies, etc).
• are not breaking changes.

Documentation

• My changes do not require a change to the project documentation.
• My changes require a change to the project documentation.
• If yes to above: I have updated the documentation accordingly.

Automated tests

• My changes can not or do not need to be tested.
• My changes can and should be tested by unit and/or integration tests.
• If yes to above: I have added tests to cover my changes.
• If yes to above: I have taken care to cover edge cases in my tests.
• All new and existing tests passed.

[glowcloud]

Thanks for the changes!

Please take a look at my comments.

[jux61]

Are you expecting something else from me?

[glowcloud]

We are investigating this further, as there might be some other related issues. We will let you know if there are any other changes needed.

[char0n]

LGTM

[glowcloud]

LGTM!