Attach (recommended) or Link to PDF file here:
[PDFBOX-5275-p5.pdf](https://github.com/mozilla/pdf.js/files/7109095/PDFBOX-5275-p5.pdf)

Configuration:
- Web browser and its version: FF 91.0.2
- Operating system and its version: Windows 10.0.19043.1165
- PDF.js version: latest (tried with https://mozilla.github.io/pdf.js/web/viewer.html )

Steps to reproduce the problem:
1. open the file
2.

What is the expected behavior? Displays a plant

What went wrong? Displays blank page

See also
https://issues.apache.org/jira/browse/PDFBOX-5275
which had the same problem, the cause was bad handling of an empty OCGs entry

![grafik](https://user-images.githubusercontent.com/6665575/132079956-c48921bf-6dbb-4e89-886e-4301d955ee35.png)


if (!this._groups.has(id)) {
      warn(`Optional content group not found: ${id}`);
      return;
    }
    this._groups.get(id).visible = !!visible;
  }
  getOrder() {
    if (!this._groups.size) {
      return null;
    }
    if (this._order) {
      return this._order.slice();
    }
    return Array.from(this._groups.keys());
  }
  getGroups() {
    return this._groups.size > 0 ? objectFromMap(this._groups) : null;
  }
  getGroup(id) {
    return this._groups.get(id) || null;
  }
}
export { OptionalContentConfig };