how to sort array in ruby if i have nil object inside array?

how to sort array if i have array like this in ruby?

example :

my_array = ["12 months", "13 months", nil, nil, "12"]

i want get result like this :

my_array.sort_by { |x| x || "Z" }=> ["12", "12 months", "13 months", nil, nil]
 my_array = ["12", "12 months", "13 months", nil, nil]


Handle the nil, this will get you close...
2.1.2 :010 > my_array.sort { |x,y| x && y ? (x <=> y) : (x ? -1 : 1) } => ["12", "12 months", "13 months", nil, nil]