xasharma Looks like the error comes from the-turk/flarum-diff requesting the old content from a post that is being hidden. From the first line, looks like that post is an event post - it doesn't have a text content.
This could theoretically be fixed by not hiding event posts (not sure Flarum even allows doing that in the front-end).
Otherwise the diff extension would have to fix it directly.
This is what I'm assuming from looking at the code - didn't try to reproduce the issue. But it's related to event posts & the diff ext.
