fix(common)!: when transforming optional boolean parameters on ValidationPipe

[micalevisk]

• 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: the issue #10246 is broader than what this PR address. For optional boolean values, when they are not supplied, the value is parsed to false

What is the new behavior?

(using ValidationPipe({ transform: true }))

This only fixes(?) the following use case:

@Query('foo') foo?: boolean

@Param('foo') foo?: boolean

now leads to foo === undefined if no query/path parameter for foo key was supplied instead of always failing back to false. Note that marking them as optional doesn't matter

Does this PR introduce a breaking change?

• Yes
• No
• Maybe - if people are not treating optional values properly, since, strictly speaking, if the request doesn't have some field (a expected boolean one), the value of that field should be undefined instead of false (unless this was a design decision for ValidationPipe when dealing with primitive values). If this introduces a breaking change, you can close it. If they want to model false as the default value, they should use this:

@Query('foo', new DefaultValue(false)): foo = false

[coveralls]

Pull Request Test Coverage Report for Build b72a66f9-002f-4c4f-a4a0-6cd60f2101b6

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 93.411%

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Totals
Change from base Build 6cae7f16-f5dd-4f5d-a093-b62a08f9388d:	0.002%
Covered Lines:	6209
Relevant Lines:	6647

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💛 - Coveralls

[damhungthinh]

May I know when this fixed will be release?
I'm facing with this transform issue too: optional params will be fallback to default value.

Thanks.

[micalevisk]

@damhungthinh it will probably be released with nestjs v10

I have no clue on when tho. Sorry.