npm run dev: TypeError in plugin "gulp-pug" - Cannot read property 'call' of undefined

[wscherphof]

[20:22:04] 'buildPug' errored after 490 ms
[20:22:04] TypeError in plugin "gulp-pug"
Message:
    docs/src/layouts/page.pug:11
    9| 
    10|             +mdc-top-app-bar__section()(align='end')
  > 11|                 +mdc-top-app-bar__action-item()(element='a' href='https://pugjs.org' target='_blank' title='Pug docs')
    12|                     img(src='https://cdn.rawgit.com/pugjs/pug-logo/eec436cee8fd9d1726d7839cbe99d1f694692c0c/SVG/pug-final-logo-_-colour-128.svg')
    13|                 +mdc-top-app-bar__action-item('code')(element='a' href='https://github.com/olegpolyakov/mdc-pug' target='_blank' title='Source code')
    14|                 +mdc-top-app-bar__action-item('forum')(element='a' href='https://github.com/olegpolyakov/mdc-pug/discussons' target='_blank' title='Discussions')

Cannot read property 'call' of undefined
Details:
    path: docs/src/layouts/page.pug
    fileName: /home/wouter/github.com/wscherphof/mdc-pug/docs/src/index.pug
    domainEmitter: [object Object]
    domainThrown: false

When I comment out the line, and the next similar ones, the build succeeds:

            +mdc-top-app-bar__section()(align='end')
                //- +mdc-top-app-bar__action-item()(element='a' href='https://pugjs.org' target='_blank' title='Pug docs')
                //-     img(src='https://cdn.rawgit.com/pugjs/pug-logo/eec436cee8fd9d1726d7839cbe99d1f694692c0c/SVG/pug-final-logo-_-colour-128.svg')
                //- +mdc-top-app-bar__action-item('code')(element='a' href='https://github.com/olegpolyakov/mdc-pug' target='_blank' title='Source code')
                //- +mdc-top-app-bar__action-item('forum')(element='a' href='https://github.com/olegpolyakov/mdc-pug/discussons' target='_blank' title='Discussions')
                //- +mdc-top-app-bar__action-item('bug_report')(element='a' href='https://github.com/olegpolyakov/mdc-pug/issues' target='_blank' title='Issues')