fix(schema): allow empty array for required field with minItems

[spiderocious]

Fixes a bug where a required array property fails validation when given an
empty array, even though the schema explicitly allows it via minItems: 0.
A required group-array with min: 0 could never be submitted empty.

Changes Made

• src/validation/schema.ts

  • In the required check, an empty array is no longer automatically treated
    as a missing value when the field schema declares minItems. In that case
    the array counts as present, and its length is validated by minItems
    (which runs separately) rather than by required.
  • Behaviour is unchanged for required arrays that do not declare
    minItems: an empty array is still treated as missing, preserving existing
    behaviour.

• test/validation/required_field.test.ts

  • Added a test that a required array with minItems: 0 accepts an empty array.
  • Added a test that a required array with minItems: 1 reports a minItems
    error (not a required error) for an empty array, confirming length is
    still enforced by the right mechanism.
  • Added a test that a required array without minItems still treats an empty
    array as missing.

Related Issues/PRs

Fixes #247

Checklist

• I have read the Contributing Guidelines and followed them.
• Unit tests were added.

---

Note

Medium Risk
Changes core required-field semantics for all required arrays (not only minItems: 0), which may alter validation for forms that relied on empty [] triggering "Required field".

Overview
Fixes validation so required on array properties no longer fails when the value is []. In schema.ts, the required-key filter used to treat empty arrays like missing fields; arrays (including empty) are now always considered present, with comments pointing authors to minItems for non-empty requirements.

Tests were updated: a required list: [] case in array field tests now expects no error, and required_field.test.ts adds coverage for empty vs populated arrays, minItems: 0 / 1, and required arrays without minItems (empty array valid; missing key still Required field).

^{Reviewed by Cursor Bugbot for commit 05b9fd4. Bugbot is set up for automated code reviews on this repo. Configure here.}

[spiderocious]

@sandrina-p @danielcardoso5 please review

[sandrina-p]

bug: This is wrong (an existing bug). By default an empty array should NOT be treated as a missing required value. I confirmed in the jsonschemalint.com

Simple JSON Schema:

{
  "type": "object",
  "additionalProperties": false,
  "properties": {
    "name": { "type": "string" },
    "browser": {
      "title": "Browsers",
      "type": "array"
    }
  },
  "required": [
    "browser"
  ]
}

So we should adapt the code, tests and comments for both scenarios.

[spiderocious]

Thanks for the review feedback, @sandrina-p , I'll address this by simplifying the check so an empty array always counts as present, and I'll update the comments and tests (including the pre-existing one in array.test.ts) to match. Pushing the fix shortly.

[spiderocious]

I've made the changes, please check again. @sandrina-p