check early for non-scalar default_fill_value
Broken off of an in-progress division-by-zero branch
is there an issue for this? I guess currently this raises but its an incorrect description of the error? > is there an issue for this? I guess currently this raises but its an incorrect description of the error?

ATM this raises once it gets passed to SparseArray.  The actual bug this fixes is the `fill_value = func(...)` on 471. thanks