Attach (recommended) or Link to PDF file here:
issue13500 (in test corpus)

This regressed when landing #13566. 

What is the expected behavior? (add screenshot)
<img width="664" alt="image" src="https://user-images.githubusercontent.com/942640/122467522-7bc8aa80-cf6f-11eb-9d4d-311eb7c64fb2.png">


What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/942640/122467565-85eaa900-cf6f-11eb-9c10-8a8686ed440c.png)


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 {