3X5ZCEPZDO2UYKQHX5YN7DC6J2WPHGR6X736NRF7QMLSUVUBYZOAC
let channel = txn.load_channel(&channel_name)?.unwrap();
txn.archive(&repo.changes, &channel, &mut tarball)?
if let Some(channel) = txn.load_channel(&channel_name)? {
txn.archive(&repo.changes, &channel, &mut tarball)?
} else {
bail!("No such channel: {:?}", channel_name);
}