Github user willb commented on the pull request:
https://github.com/apache/spark/pull/1136#issuecomment-46640150
So I've added a cast in cases in which non-boolean expressions are supplied
to having expressions. It appears that `Cast(_, BooleanType)` isn't
idempotent, though -- if you apply it to a Boolean (say, `x > 4`), it will
translate that to `NOT ((x > 4) = 0)`. This seems like a bug, but it's
possible that I'm missing the reason why it should work that way. Should I
change `Cast` so that casting an _X_ to _X_ is a no-op?
(Checking the type of a variable during parse doesn't work, so I wind up
with a different exception in examples like the one you posted. I'll either
need to fix the behavior of `Cast` or delay adding the cast until I have type
information.)
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