fix: handle undefined or empty rules in validator

[chantouchsek]

Linked Issue

Fixed #1104

[Copilot]

Pull request overview

This PR fixes issue #1104 by adding logic to handle undefined and empty string rules in the validator's _parseRulesDefault method.

• Restructured the conditional logic to explicitly handle array, undefined/empty string, and other types separately
• Added filter(Boolean) to remove empty strings from pipe-separated rules
• Added a test case to verify undefined and empty rules don't cause errors

Reviewed changes

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

File	Description
src/main.ts	Modified _parseRulesDefault to handle undefined and empty string rules by converting them to empty arrays, and added filtering to remove empty values from pipe-separated rule strings
tests/validator.spec.ts	Added test case to verify that undefined and empty string rules are handled without errors

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