Undefined error during static HTML generation

[JJdeGroot]

Description of problem

URL to affected spec or repo:

https://github.com/w3c/matf

What happened (e.g., it crashed)?:

The "Generate Static HTML" step failed, with an "undefined" error.

Expected behavior (e.g., it shouldn't crash):

The step should succeed

Optional, steps to reproduce:

It might be related to merging Pull Requests?

https://github.com/w3c/matf/actions/runs/18904396745/job/53959060411#step:7:520

Respec 35.6.0

$ respec -s "http://localhost:3000/index.html" -o "index.html.built.html" --verbose -t 20 -e
      [INFO] [Timeout: 20000ms] Processing resource: http://localhost:3000/index.html ...
      [INFO] [Timeout: 20000ms] Launching browser
      [INFO] [Timeout: 0ms] Navigating to http://localhost:3000/index.html
      [INFO] [Timeout: 0ms] Navigation complete.
      [INFO] [Timeout: 0ms] Using ReSpec v35.6.0
      [INFO] [Timeout: 0ms] Processing ReSpec document...
      [FATAL] Error: 
      😭  Sorry, there was an error generating the HTML. Please report this issue!
      Specification: http://localhost:3000/index.html
      ReSpec version: 35.6.0
      File a bug: https://github.com/speced/respec/
      Error: undefined
      
          at generateHTML (file:///home/runner/work/_actions/w3c/spec-prod/v2/node_modules/.pnpm/respec@35.6.0_typescript@5.4.5/node_modules/respec/tools/respecDocWriter.js:233:11)
          at async toHTML (file:///home/runner/work/_actions/w3c/spec-prod/v2/node_modules/.pnpm/respec@35.6.0_typescript@5.4.5/node_modules/respec/tools/respecDocWriter.js:100:18)
          at async run (file:///home/runner/work/_actions/w3c/spec-prod/v2/node_modules/.pnpm/respec@35.6.0_typescript@5.4.5/node_modules/respec/tools/respec2html.js:271:38)
          at async file:///home/runner/work/_actions/w3c/spec-prod/v2/node_modules/.pnpm/respec@35.6.0_typescript@5.4.5/node_modules/respec/tools/respec2html.js:232:5
    Command `respec -s "http://localhost:3000/index.html" -o "index.html.built.html" --verbose -t 20 -e` failed with exit code: 1.

https://github.com/w3c/matf/actions/runs/18148560135/job/51654868717

ReSpec 35.5.1

[INFO] Build respec document "index.html" (common)…
    $ respec -s "http://localhost:3000/index.html" -o "index.html.built.html" --verbose -t 20 -e
      [INFO] [Timeout: 20000ms] Processing resource: http://localhost:3000/index.html ...
      [INFO] [Timeout: 20000ms] Launching browser
      [INFO] [Timeout: 0ms] Navigating to http://localhost:3000/index.html
      [INFO] [Timeout: 0ms] Navigation complete.
      [INFO] [Timeout: 0ms] Using ReSpec v35.5.1
      [INFO] [Timeout: 0ms] Processing ReSpec document...
      [FATAL] Error: 
      😭  Sorry, there was an error generating the HTML. Please report this issue!
      Specification: http://localhost:3000/index.html
      ReSpec version: 35.5.1
      File a bug: https://github.com/speced/respec/
      Error: undefined
      
          at generateHTML (file:///home/runner/work/_actions/w3c/spec-prod/v2/node_modules/.pnpm/respec@35.5.1_typescript@5.4.5/node_modules/respec/tools/respecDocWriter.js:233:11)
          at async toHTML (file:///home/runner/work/_actions/w3c/spec-prod/v2/node_modules/.pnpm/respec@35.5.1_typescript@5.4.5/node_modules/respec/tools/respecDocWriter.js:100:18)
          at async run (file:///home/runner/work/_actions/w3c/spec-prod/v2/node_modules/.pnpm/respec@35.5.1_typescript@5.4.5/node_modules/respec/tools/respec2html.js:271:38)
          at async file:///home/runner/work/_actions/w3c/spec-prod/v2/node_modules/.pnpm/respec@35.5.1_typescript@5.4.5/node_modules/respec/tools/respec2html.js:232:5
    Command `respec -s "http://localhost:3000/index.html" -o "index.html.built.html" --verbose -t 20 -e` failed with exit code: 1.

When triggering a new action from main branch, it succeeded: https://github.com/w3c/matf/actions/runs/18904864816/job/53960572833