Attach (recommended) or Link to PDF file here:  [test.pdf](https://akmer.aikucun.com/a94a8fe5ccb19ba61c4c0873d391e987982fbbd3_1616477914120_83.pdf)


Configuration:
- Web browser and its version: chrome 87.0.4280.88
- Operating system and its version: windows10
- PDF.js version: 2.6.347
- Is a browser extension:

Steps to reproduce the problem:
1. just open 

What is the expected behavior? (add screenshot)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/17724610/112087066-473f8f80-8bc8-11eb-8efb-56139ec42a9c.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

? stringToPDFString(group.get("Intent"))
            : null,
        });
      }
      config = this._readOptionalContentConfig(defaultConfig, groupRefs);
      config.groups = groups;
    } catch (ex) {
      if (ex instanceof MissingDataException) {
        throw ex;
      }
      warn(`Unable to read optional content config: ${ex}`);
    }
    return shadow(this, "optionalContentConfig", config);
  }
  _readOptionalContentConfig(config, contentGroupRefs) {
    function parseOnOff(refs) {
      const onParsed = [];
      if (Array.isArray(refs)) {
        for (const value of refs) {
          if (!isRef(value)) {
            continue;
          }
          if (contentGroupRefs.includes(value)) {
            onParsed.push(value.toString());
          }
        }
      }
      return onParsed;
    }
    function parseOrder(refs, nestedLevels = 0) {