hi @GeremyHanjra can you give more information on your setup where this error occurs?

I have encountered this error too. Perhaps this could help:

Version: 3.11.4
JS Console:

modernizr.js:6623 Uncaught TypeError: Cannot read property 'removeChild' of null
    at Object.fn (modernizr.js:6623)
    at testRunner (modernizr.js:143)
    at modernizr.js:9901
    at modernizr.js:9917

Attached generated modernizr.js (with npx modernizr): modernizr.zip

Location: Modernizr.addTest('localizednumber', function() {...

    /* cleanup */
    body.removeChild(div);
    if (body.fake) {
      body.parentNode.removeChild(body);
    }

A null check fixes the issue:

    /* cleanup */
    body.removeChild(div);
    if (body.fake && body.parentNode) {
      body.parentNode.removeChild(body);
    }

Also issue goes away if I remove "forms/inputnumber-l10n" from configuration.

Thanks for the hint @arhanta I added your code fix to the v3 brach. Could you check it out and see if it fixes your issue?

Looks good. I did wonder if there are any other places in code where such a check might be needed, and I see you found one more.

Am I somehow using Modernizr improperly, that such a thing (body without parent) happens?

Good question but I am not that deep into the code. Are you using modernizr just simply on your page or do you add it via iframe or anything special?

Apologies for not answering this. I will take advantage of the necro and mention that we are just including modernizr in the page, nothing fancy.
I think this can be closed.

@damian-cell your issue should be fixed (if you need the test) since v3.11.5