Question

If the results is nil then I get NoMethodError - undefined method 'length' for nil:NilClass:

Is there any way I don’t have to use two conditions? I thought that ruby won’t evaluate the second part of the condition in case results is empty because the condition can be never true.

if (not results.empty? && results[-1].length == 2)
  (4-results[-1].length).times {|i| results[-1] << ""}
end

Answer 1

In ruby the not operator has lower precedence than && so your code is being interpreted as

not (results.empty? && (results[-1].length == 2))

You probably want to use the ! operator instead which does the same as not but has higher precedence.