def trim_lines(lines)
      new_lines = lines.dup
      while new_lines[-1] && new_lines[-1].strip.empty?
        new_lines.pop
      end
      new_lines
    end
def trim_lines(lines)
      new_lines = lines.dup
      while new_lines[-1] && new_lines[-1].strip.empty?
        new_lines.pop
      end
      new_lines
    end
remove elements at the back of `lines` if element is empty string
 (`lines` should be Array of String.)