This error occurs in all interactions with the Change Request, whether to create, review or publish a page. I noticed this error when after an update from version 1.13.2 to 1.15 the timeline description stopped appearing. When restarting the server, the timeline returned but the error continued. And another Xwiki with Change Request version 1.13.2 also has this error in the log
[2024-07-02 14:22:47] [info] 2024-07-02 14:22:47,845 [http-nio-8080-exec-2 - http://localhost:8080/xwiki/bin/view/ChangeRequest/Data/aa-5a0fc6bf-e8c3-4b69-bcd9-82ad7640b990/] ERROR o.a.v.rendering
- Left side ($documentPropertiesSummary.modified) of comparison operation has null value at environment:/templates/diff_macros.vm[line 421, column 45]
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