`-if-let` treats list with one nil element as nil

[phst]

Consider:

(-if-let ((a b) '(1 2)) (list a b) 'else)
(1 2)

(-if-let ((a b) '(1 nil)) (list a b) 'else)
else

I think the behavior in the second case is a bug; the VAL is not nil, yet the else branch is taken.