Attach (recommended) or Link to PDF file here:
PDF from #4106, https://mail.gnome.org/archives/evince-list/2013-November/pdfNC0hkVW67a.pdf.

Steps to reproduce the problem:
1. Open the PDF

What is the expected behavior?
![immagine](https://user-images.githubusercontent.com/1616846/121865567-67ca4200-ccfe-11eb-8673-1d6e863fc8d5.png)

What went wrong?
The PDF doesn't load, `TypeError: can't access property Symbol(), match is null` error is logged in the console.
}
    if (!ui.attributes.class) {
      ui.attributes.class = [];
    }
    switch (this.caption.placement) {
      case "left":
        ui.children.splice(0, 0, caption);
        ui.attributes.class.push("xfaLeft");
        break;
      case "right":
        ui.children.push(caption);
        ui.attributes.class.push("xfaLeft");
        break;
      case "top":
        ui.children.splice(0, 0, caption);
        ui.attributes.class.push("xfaTop");
        break;
      case "bottom":
        ui.children.push(caption);
        ui.attributes.class.push("xfaTop");
        break;
      case "inline":
        
        ui.attributes.class.push("xfaLeft");
        break;
    }
    return HTMLResult.success(createWrapper(this, html), bbox);
  }
}
class Fill extends XFAObject {