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.
constructor(attributes) {
    super(TEMPLATE_NS_ID, "stipple",  true);
    this.id = attributes.id || "";
    this.rate = getInteger({
      data: attributes.rate,
      defaultValue: 50,
      validate: x => x >= 0 && x <= 100,
    });
    this.use = attributes.use || "";
    this.usehref = attributes.usehref || "";
    this.color = null;
    this.extras = null;
  }
  [$toStyle](bgColor) {
    const alpha = this.rate / 100;
    return Util.makeHexColor(
      Math.round(bgColor.value.r * (1 - alpha) + this.value.r * alpha),
      Math.round(bgColor.value.g * (1 - alpha) + this.value.g * alpha),
      Math.round(bgColor.value.b * (1 - alpha) + this.value.b * alpha)
    );
  }
}
class Subform extends XFAObject {