fix: preserve zero results from AVERAGEIF

[Tobiadefami]

Context

AVERAGEIF returned a #DIV/0! error when matching values produced a valid average of 0.

This happened because the result used a logical OR fallback, which treated 0 as if no average had been
calculated. This change uses nullish coalescing so that only an absent result produces #DIV/0!, while a
valid zero is returned normally.

How did you test your changes?

Added a regression test where the matching values are -1 and 1, producing an average of 0.

The test was verified to fail with #DIV/0! before the fix and pass with 0 after the fix.

I also ran:

• The focused AVERAGEIF test suite: all 14 tests passed.
• npm run bundle:cjs: TypeScript and the CommonJS build completed successfully.
• Targeted linting: no errors.

Types of changes

• Breaking change (a fix or a feature because of which an existing functionality doesn't work as
  expected anymore)
• New feature or improvement (a non-breaking change that adds functionality)
• Bug fix (a non-breaking change that fixes an issue)
• Additional language file, or a change to an existing language file (translations)
• Change to the documentation

Related issues:

None.

Checklist:

• I have reviewed the guidelines about [Contributing to HyperFormula](https://
  hyperformula.handsontable.com/guide/contributing.html) and I confirm that my code follows the code style of
  this project.
• I have signed the Contributor License Agreement.
• My change is compliant with the [OpenDocument](https://docs.oasis-open.org/office/OpenDocument/v1.3/
  os/part4-formula/OpenDocument-v1.3-os-part4-formula.html) standard.
• My change is compatible with Microsoft Excel.
• My change is compatible with Google Sheets.
• I described my changes in the [CHANGELOG.md](https://github.com/handsontable/hyperformula/blob/master/
  CHANGELOG.md) file.
• My changes require a documentation update.
• My changes require a migration guide.

---

Note

Low Risk
Single-expression change in AVERAGEIF error handling with no auth, data, or API surface impact.

Overview
AVERAGEIF incorrectly returned #DIV/0! when the matched cells produced a true average of 0 (e.g. values -1 and 1).

The return path in ConditionalAggregationPlugin switched from logical OR (||) to nullish coalescing (??) when falling back to #DIV/0!. A computed 0 is no longer treated as “no result”; only a missing average (no matching count) still yields the division-by-zero error.

The unreleased CHANGELOG entry documents this fix.

^{Reviewed by Cursor Bugbot for commit 8775411. Bugbot is set up for automated code reviews on this repo. Configure here.}

[cla-external-contractor-signup]

@Tobiadefami thanks for the pull request. No CLA step needed here — our records show you signed the Contributor License Agreement on 2026-07-31. That signature came from our previous signing form and has been carried over, so there is nothing for you to re-sign.

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
✅ Deployment successful! View logs	hyperformula-docs	8775411	Commit Preview URL Branch Preview URL	Aug 13 2026, 10:00 AM

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.31%. Comparing base (61ead73) to head (8775411).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1733   +/-   ##
========================================
  Coverage    97.31%   97.31%           
========================================
  Files          195      195           
  Lines        15719    15719           
  Branches      3455     3455           
========================================
  Hits         15297    15297           
  Misses         414      414           
  Partials         8        8           

Files with missing lines	Coverage Δ
...interpreter/plugin/ConditionalAggregationPlugin.ts	100.00% <100.00%> (ø)

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[github-actions]

Performance comparison of head (8775411) vs base (61ead73)

                                     testName |    base |    head | change
--------------------------------------------------------------------------
                                      Sheet A |  364.54 |  369.09 | +1.25%
                                      Sheet B |  114.34 |   112.8 | -1.35%
                                      Sheet T |  101.16 |   99.24 | -1.90%
                                Column ranges |  495.36 |  496.93 | +0.32%
                                Sorted lookup | 15311.6 | 14605.6 | -4.61%
Sheet A:  change value, add/remove row/column |    10.1 |   10.27 | +1.68%
 Sheet B: change value, add/remove row/column |   96.93 |   98.75 | +1.88%
                   Column ranges - add column |  123.12 |  125.53 | +1.96%
                Column ranges - without batch |  406.09 |  389.48 | -4.09%
                        Column ranges - batch |  103.88 |   95.44 | -8.12%