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 (this.exData) {
      return this.exData[$content][$text]().trim();
    }
    for (const name of Object.getOwnPropertyNames(this)) {
      if (name === "image") {
        continue;
      }
      const obj = this[name];
      if (obj instanceof XFAObject) {
        return (obj[$content] || "").toString().trim();
      }
    }
    return null;
  }
  [$toHTML](availableSpace) {
    for (const name of Object.getOwnPropertyNames(this)) {
      const obj = this[name];
      if (!(obj instanceof XFAObject)) {
        continue;
      }
      return obj[$toHTML](availableSpace);
    }
    return HTMLResult.EMPTY;
  }
}
class Variables extends XFAObject {