It looks like typo in PolygonGeometryUpdater.js

1. A concise explanation of the problem you're experiencing.

line 346 and then


4. The Cesium version you're using, your operating system and browser.

Cesium 1.55

Looks like you’re right. Feel free to fix that yourself if you’d like to open a PR and be an official contributor!

Contributing guide:

Thank you for your advice.
I will read the guide carefully.