Allows comparing arrays with nils

array_nil_compare_hack.rb

#usage
a = [1,2]
b = [1,nil]
a.extend(ArrayWithNilCompareHack)
b.extend(ArrayWithNilCompareHack)
a<=>b # works

# code
module ArrayWithNilCompareHack
  def <=>(other)
    size_compare = self.size <=> other.size
    return size_compare if size_compare.nonzero?
    
    each_index do |i|
      next if self[i].nil? && other[i].nil?
      return -1 if self[i].nil?
      return 1 if other[i].nil?
      normal = self[i] <=> other[i]
      next if normal==0
      return normal
    end

    0
  end
end