fix(i18n): handle missing date formats

[viktorkombov]

Closes #17493

Description

Prevents Angular 22.1 from throwing when a date format is null, undefined, or empty. Preserves the previous empty-string behavior and adds regression coverage.

Motivation / Context

Type of Change (check all that apply):

• Bug fix
• New functionality
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (no functional changes)
• Documentation
• Demos
• CI/CD
• Tests
• Changelog
• Skills/Agents

Component(s) / Area(s) Affected:

How Has This Been Tested?

• Unit tests
• Manual testing
• Automated e2e tests

Test Configuration:

• Angular version:
• Browser(s):
• OS:

Screenshots / Recordings

Checklist:

• All relevant tags have been applied to this PR
• This PR includes unit tests covering all the new code (test guidelines)
• This PR includes API docs for newly added methods/properties (api docs guidelines)
• This PR includes feature/README.MD updates for the feature docs
• This PR includes general feature table updates in the root README.MD
• This PR includes CHANGELOG.MD updates for newly added functionality
• This PR contains breaking changes
• This PR includes ng update migrations for the breaking changes (migrations guidelines)
• This PR includes behavioral changes and the feature specification has been updated with them
• Accessibility (ARIA, keyboard navigation, focus management) has been verified

[Copilot]

Pull request overview

Fixes a regression in Ignite UI’s BaseFormatter.formatDate() when running under Angular 22.1+ by preventing Angular’s formatDate() from being called with a missing/empty format string (which can throw due to .length validation added upstream).

Changes:

• Broadened BaseFormatter.formatDate()’s format parameter type to allow null | undefined and added a guard to return '' when the format is missing/empty.
• Added a regression unit test covering undefined, null, and '' format inputs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
projects/igniteui-angular/core/src/core/i18n/formatters/formatter-base.ts	Avoids calling Angular formatDate() when format is missing/empty by widening type + adding a guard.
projects/igniteui-angular/core/src/core/i18n/formatters/formatter-base.spec.ts	Adds regression coverage for missing/empty format values returning an empty string.

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[ivanvpetrov]

The tests now pass. Judging by that the fix is ok.
What I'm not sure of, is if this fix changes any behavior in an unwanted way.

[viktorkombov]

The tests now pass. Judging by that the fix is ok.
What I'm not sure of, is if this fix changes any behavior in an unwanted way.

@ivanvpetrov, good point. I checked the affected paths.

The only runtime change is in BaseFormatter when the value is present but the format is null, undefined, or empty. Angular 22.0 returned an empty string in that case, while Angular 22.1 now throws during format validation. The guard restores the previous behavior.

Valid formats still go directly through Angular’s formatDate, and nullish values still return an empty string. IntlFormatter has no runtime behavior change; only its parameter type was widened to match the base contract.

Therefore, no behavior should change for valid inputs. The fix only prevents the new Angular 22.1 exception for missing formats.