This is a submission for DEV's Summer Bug Smash: Clear the Lineup powered by Sentry.
You are migrating a 50,000-message Slack workspace to Zulip. Somewhere around message 31,000 the import dies with KeyError: 'ts'. Annoying, but here is the uncomfortable part: that is the lucky outcome. The unlucky one is "ts": "NaN", where nothing dies, nothing warns, and your company's message history quietly comes out in the wrong order.
TL;DR: Zulip's Slack importer used float(message["ts"]) unguarded, both as a sort key and as date_sent. One message with a missing or malformed ts aborted the entire import; a non-finite value like "NaN" did not even raise, it silently broke the sort. My fix (zulip/zulip#39813) skips such messages with a warning and requires ts to parse to a finite float via math.isfinite. The regression test fails with KeyError: 'ts' on the old code.
Project Overview
Zulip is an open-source team chat server (Django/Python, ~25k stars) with an unusually strict engineering culture: near-total backend test coverage, strict mypy, and a commit discipline of "each commit is a minimal coherent idea".
