We are getting an empty glyphData object (thus a null glyph (0)) when the input character is the object replacement character (0xFFFC).
If such input is decorated with text-emphasis-marker, this will cause the marker not to be painted after https://github.com/WebKit/WebKit/pull/12471 is merged.

This is because, the null glyph gets replaced by the deleted glyph (0xFFFF) and after the PR is merged, we no longer will draw markers for associated deleted glyphs.

How to reproduce it:


<p class="foo">X</p>

.foo {
  writing-mode:vertical-lr;
  text-combine-upright:all;
  text-emphasis:filled;
}