This occurs in the DVR Web UI on the latest pre-release v2021.10.29.2303.
When saving Library Collections with a Smart Rule, it seems that a blank Image URL field is not properly handled, based on the error in the browser dev console:
Uncaught TypeError: Cannot read properties of undefined (reading 'push')
at N1 (ContentImage.js:88)
at onClick (ContentImage.js:326)
at Object.OZ1 (react-dom.production.min.js:14)
at UZ1 (react-dom.production.min.js:14)
at FZ1 (react-dom.production.min.js:14)
at R31 (react-dom.production.min.js:15)
at $Z1 (react-dom.production.min.js:52)
at ZI (react-dom.production.min.js:51)
at mg (react-dom.production.min.js:52)
at E81 (react-dom.production.min.js:56)
To reproduce, add a new Movie or Show Collection with just a title, blank image URL and default sort. Then add any Smart Rule, e.g., Genres + Any + Action in the Simple Mode Rule Editor and click Save. Then Rule Editor closes and the entire page freezes. To trigger the above console error, click on Edit Smart Rule or almost anywhere below it, such as on a movie/show thumbnail. Reloading the page unfreezes it, but then after editing existing collections without an Image URL and clicking Save, the entire page freezes again as before.
I would like to create library collections first without images and then add them later.