Fix/10017 parse file pipe builder

[thiagomini]

PR Checklist

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• 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: #10017

What is the new behavior?

Now we can specify if a given file parameter is required in the ParseFilePipeBuilder or in the ParseFilePipe:

@UploadedFile(
  new ParseFilePipeBuilder()
    .addFileTypeValidator({
      fileType: 'json',
    })
    .build({
      fileIsRequired: false,
    }),
)
file?: Express.Multer.File,

With that, when a file is explicitly set to be optional, the ParseFileValidator won't throw an error. On the other hand, when the file is required (default behavior), it will now throw a 400 error.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[thiagomini]

Some minor fixes I'll work on soon

[coveralls]

Pull Request Test Coverage Report for Build 0a52d60b-a134-4623-891a-69fd95493980

• 7 of 7 (100.0%) changed or added relevant lines in 1 file are covered.
• 13 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.006%) to 94.029%

---

Files with Coverage Reduction	New Missed Lines	%
packages/core/router/router-explorer.ts	13	79.88%

Totals
Change from base Build 8c0de0f2-40f8-43a4-81d6-106b72b5ecee:	0.006%
Covered Lines:	6063
Relevant Lines:	6448

---

💛 - Coveralls

[micalevisk]

Suggested change

	* Defines if file parameter is optional. Default is false.
	*/
	* Defines if file parameter is optional.
	* @default false
	*/

[micalevisk]

what about

Suggested change

	fileIsOptional?: boolean;
	required?: boolean;

and then the default will be true.

[thiagomini]

changed to required semantic, but I maintained the full word fileIsRequired to be explicit here. In the consumer side, when creating a ParseFilePipe, I think it's worth it to specify what is required:

const parseFilePipe = new ParseFilePipe({
  validators: [],
  fileIsRequired: false,
});

[thiagomini]

@kamilmysliwiec waiting for your review here. If this is accepted, I suppose we'll have to update the docs as well

[kamilmysliwiec]

lgtm