fix(common): fallback to empty string for enums when validating (swc builder)

[kamilmysliwiec]

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?

Issue Number: #12680

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 23759b43-a233-4f4f-9d66-b773604ecffe

Details

• 3 of 6 (50.0%) changed or added relevant lines in 1 file are covered.
• 29 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.04%) to 91.952%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/common/pipes/validation.pipe.ts	3	6	50.0%

Files with Coverage Reduction	New Missed Lines	%
packages/core/injector/injector.ts	29	84.34%

Totals
Change from base Build 1d36b27a-0a3e-4f95-b141-14fcdc7e1b87:	-0.04%
Covered Lines:	6810
Relevant Lines:	7406

---

💛 - Coveralls

[JoCat]

Now there are no previous errors. But only the query gives 400 in the condition when the parameter is not specified, even though it is optional.

UPD
A little bit of research:
Before the fix, not passing a value caused a 500 error in the browser and a TypeError in the code. Passing a value that was not in the enum sample resulted in a 400 error, passing the correct value was handled correctly.
After the fix, failure to pass a value causes the same 400 error as with an invalid enum value.