def ary_to_sentence(ary, empty_sentence = nil)
      case ary.length
      when 0 then empty_sentence.to_s
      when 1 then ary.first
      when 2 then ary.join(' and ')
      else
        *ary, last_element = ary
        ary_to_sentence([ary.join(', '), last_element])
      end
    end
def ary_to_sentence(ary, empty_sentence = nil)
      case ary.length
      when 0 then empty_sentence.to_s
      when 1 then ary.first
      when 2 then ary.join(' and ')
      else
        *ary, last_element = ary
        ary_to_sentence([ary.join(', '), last_element])
      end
    end
Constructs a sentence from array elements, connecting them with commas
 and conjunctions.

 @param ary [Array<String>] the array
 @param empty_sentence [String, nil] the sentence to return if the array
                                     is empty
 @return [String] the constructed sentence