fix(microservices): getOptionsProp doesn't ignore a non-empty value

[IKatsuba]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

ClientProxy.getOptionsProp returns undefined instead of non-empty value (0, an empty string, etc)

Issue Number: N/A

What is the new behavior?

ClientProxy.getOptionsProp returns a non-empty value (0, an empty string, etc)

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 0deb9659-9cfb-40d4-9cfc-17c5b7140669

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.788%

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Totals
Change from base Build 8bf86286-b462-4455-92cd-c0e58fd6edb9:	0.0%
Covered Lines:	6115
Relevant Lines:	6520

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💛 - Coveralls

[kamilmysliwiec]

Let's track this here #10549 (more info here #10549 (comment))