join is broken for events

[greenrd]

In GHCi:

Prelude FRP.Reactive.Reactive Control.Monad Control.Applicative> join $ return (empty :: Event ())
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Event: *** Exception: BothBottom

join . return should be equal to id

[greenrd]

Also, possibly related:

Prelude Control.Monad Control.Applicative FRP.Reactive.Reactive> listE [(2,())] <|> (return undefined =<< listE [(2,())]) 
Event: *** Exception: BothBottom

I think this should produce the left occurrence at least, because any occurrences coming from the right (although we know there aren't any) should be at time >=2, so the left occurrence must come first.