I don't have a good repro case for this, I hit the issue in the middle of some other code.
on like 2332 or so of master you have some code like:
`
(cond
...
(lcons? v)
(loop [u u v (seq v) cs cs]
...
)
`
This is obviously incorrect, because anything that returns true to lcons? will throw an exception with you call seq on it.
