Website sidebar section glob matching no inputs crashes pre-render in findIndexFile

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• searched the issue tracker for similar issues
• installed the latest version of Quarto CLI
• formatted my issue following the Bug Reports guide

Bug description

A website project crashes at pre-render when a sidebar section's contents is a glob that matches no project inputs and the glob's basename starts with * (for example docs/*.ipynb in a project with no notebooks).

The boundary is narrow. The same glob with at least one match renders fine. An unmatched glob whose basename has a prefix before the star, such as docs/nomatch-*.ipynb, also renders fine. The extension makes no difference. A section whose contents is a bare directory crashes identically when that directory contains no index file.

This is a regression: the same configuration built cleanly for a long time before 1.10 (it comes from the sidebar of https://github.com/AnswerDotAI/fasthtml, which renders a staged subset of inputs during README generation, so its globs can legitimately match nothing).

Steps to reproduce

Three files:

_quarto.yml:

project:
  type: website

website:
  sidebar:
    contents:
      - index.qmd
      - section: Docs
        contents: docs/*.ipynb

index.qmd and docs/a.qmd: any trivial page.

Then run quarto render. Note there is no .ipynb file anywhere, so the section glob matches nothing.

Actual behavior

ERROR: TypeError: Cannot convert undefined or null to object

Stack trace:
    at Object.keys (<anonymous>)
    at findIndexFile (file:///Applications/quarto/bin/quarto.js:146701:17)
    at nodesToEntries (file:///Applications/quarto/bin/quarto.js:146655:21)
    at sidebarItemsFromAuto (file:///Applications/quarto/bin/quarto.js:146583:16)
    at expandAutoSidebarItems (file:///Applications/quarto/bin/quarto.js:146510:31)
    at expandAutoSidebarItems (file:///Applications/quarto/bin/quarto.js:146533:31)
    at resolveSidebarItems (file:///Applications/quarto/bin/quarto.js:147918:30)
    at sidebarEjsData (file:///Applications/quarto/bin/quarto.js:147909:9)
    at async sidebarsEjsData (file:///Applications/quarto/bin/quarto.js:147894:22)
    at async initWebsiteNavigation (file:///Applications/quarto/bin/quarto.js:147263:27)
    at async Object.preRender (file:///Applications/quarto/bin/quarto.js:152689:5)

Expected behavior

The section renders empty, or a warning names the glob that matched nothing. Both match the behavior of earlier Quarto versions.

Your environment

macOS (Apple Silicon), Quarto 1.10.18 from the installer at /Applications/quarto.

Quarto check output

Quarto 1.10.18
[>] Checking environment information...
      Quarto cache location: /Users/jhoward/Library/Caches/quarto
[>] Checking versions of quarto binary dependencies...
      Pandoc version 3.10.0: OK
      Dart Sass version 1.101.0: OK
      Deno version 2.7.14: OK
      Typst version 0.15.1: OK
[>] Checking versions of quarto dependencies......OK
[>] Checking Quarto installation......OK
      Version: 1.10.18
      Path: /Applications/quarto/bin
[>] Checking basic markdown render....OK
[>] Checking Python 3 installation....OK
      Version: 3.13.2
      Jupyter: 5.9.1
[>] Checking Jupyter engine render....OK

This report was researched and written by Fable (Anthropic's Claude), with jph00's supervision.

Reproduce the failure with the three-file project described in _quarto.yml, index.qmd, and docs/a.qmd, then run quarto render. Start by tracing findIndexFile from the reported stack trace and inspect how an unmatched sidebar glob is handled; done means the project renders an empty section or emits a warning instead of crashing.