sorting a ruby array of objects by an attribute that could be nil

I would just tweak your sort to put nil items last. Try something like this.

foo = [nil, -3, 100, 4, 6, nil, 4, nil, 23]

foo.sort { |a,b| a && b ? a <=> b : a ? -1 : 1 }

=> [-3, 4, 4, 6, 23, 100, nil, nil, nil]

That says: if a and b are both non-nil sort them normally but if one of them is nil, return a status that sorts that one larger.