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)


const edges = this.edge.children.slice();
    if (edges.length < 4) {
      const defaultEdge = edges[edges.length - 1] || new Edge({});
      for (let i = edges.length; i < 4; i++) {
        edges.push(defaultEdge);
      }
    }
    const edgeStyles = edges.map(node => {
      const style = node[$toStyle]();
      style.color = style.color || "#000000";
      return style;
    });
    const widths = edges.map(edge => edge.thickness);
    const insets = [0, 0, 0, 0];
    if (this.margin) {
      insets[0] = this.margin.topInset;
      insets[1] = this.margin.rightInset;
      insets[2] = this.margin.bottomInset;
      insets[3] = this.margin.leftInset;
    }
    this[$extra] = { widths, insets };
    
    const style = Object.create(null);
    if (this.margin) {
      Object.assign(style, this.margin[$toStyle]());
    }
    if (this.fill) {