This bug didn't occur on the main branch of this repo, but on a fork which modifications are relevant to integrate this runtime into rustc.
There's more detailed explanation of modifications done in this PR: rust-lang/rust#140206
However it seems like it's not my fault, so I've decided to document it here for better or worse:
thread '<unnamed>' panicked at ~/.cargo/git/checkouts/chili-3ea47afa4e2c4ada/7358b30/src/job.rs:247:62:
called `Option::unwrap()` on a `None` value
EDIT: btw I'm an amateur on the heartbeat scheduling