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)


attributes,
      children,
    };
    const borderStyle = this.border ? this.border[$toStyle]() : null;
    const bbox = computeBbox(this, html, availableSpace);
    const ui = this.ui ? this.ui[$toHTML]().html : null;
    if (!ui) {
      Object.assign(style, borderStyle);
      return HTMLResult.success(createWrapper(this, html), bbox);
    }
    if (!ui.attributes.style) {
      ui.attributes.style = Object.create(null);
    }
    if (this.ui.button) {
      Object.assign(ui.attributes.style, borderStyle);
    } else {
      Object.assign(style, borderStyle);
    }
    children.push(ui);
    if (this.value) {
      if (this.ui.imageEdit) {
        ui.children.push(this.value[$toHTML]().html);
      } else if (!this.ui.button) {
        let value = "";
        if (this.value.exData) {
          value = this.value.exData[$text]();
        } else {
          const htmlValue = this.value[$toHTML]().html;
          if (htmlValue !== null) {
            value = htmlValue.value;