Empty sub bullet point causes next bullet point to be on the same line

[AlexDvorak]

Given the following HTML, with an empty sub bullet point as seen in the HTML below, weasyprint (v47) renders the following bullet point on the same line
but when the same HTML is rendered in Firefox, the bullet point is on its own line.
when checking inspect element, the HTML does not correct to anything else so it would appear that this is an issue with weasyprint and not bad HTML I believe.
HTML that breaks Weasyprint (Firefox does not do anything else to it)

<ul>
  <li>
    hello
    <ul>
      <li>hi</li>
      <li></li>
    </ul>
  </li>
  <li>hu</li>
</ul>

[liZe]

Thanks a lot for this report. I'm always surprised (and really disappointed) to discover really simple corner cases that are broken…

[liZe]

Well, the behavior is actually not defined by CSS, even in recent modules:

The size or contents of the marker box may affect the height of the principal block box and/or the height of its first line box, and in some cases may cause the creation of a new line box; this interaction is also not defined.

I can try to find a way to make li elements at least as high as their markers.

[liZe]

@AlexDvorak It's fixed, thanks for the report!

If anyone knows how it's implemented in other browsers, please tell me! I suppose that an empty linebox is added, but it sounds like a really big change in the DOM for a very small feature.