Problema ao usar "!" no IF

O problema é no método start que da erro no if:

 if !valid_position? map, new_position
     next
 end

Erro

N:/Ruby Project/fogefoge/fogefoge.rb:60:in `start': undefined local variable or method `position' for main:Object (NameError)
Did you mean?  new_position
        from N:/Ruby Project/fogefoge/fogefoge.rb:73:in `start_fogefoge'
        from N:/Ruby Project/fogefoge/main.rb:3:in `<main>'

eu não sei se isso é forma errada de escrita "por mais que esteja igual ao exemplo da aula" ou pode ser porque estou usando uma versão atual do ruby ou IDE ruby mine.

Código completo aqui:

require_relative "ui"

def read_map(number)
    archive = "map#{number}.txt"
    text = File.read archive
    map = text.split "\n"
end

def find_player(map)
    hero_character = "H"
    map.each_with_index do |current_line, line|
        column_hero = current_line.index hero_character
        if column_hero
          return [line, column_hero]
        end
    end
end

def calculates_new_position(hero, direction)
    hero = hero.dup
    case direction
        when "W"
            hero[0] -= 1
        when "S"
            hero[0] += 1
        when "A"
            hero[1] -= 1
        when "D"
            hero[1] += 1
    end
    hero
end

def valid_position?(map, position)
    lines = map.size
    columns = map[0].size

    broke_lines = position[0] < 0 || position[0] >= lines
    broke_columns = position[1] < 0 || position[1] >= columns

    if broke_lines || broke_columns
      return false
    end

    if map[new_position[0]][new_position[1]] == "X"
      return false
    end

    true
end

def start(nick)
    map = read_map(1)
    while true
      drawing map
      direction = asks_movement

      hero = find_player map
      new_position = calculates_new_position hero, direction
      if !valid_position? map, new_position
        next
      end

      map[hero[0]][hero[1]] =" "
      map[new_position[0]][new_position[1]] = "H"

    end
end

def start_fogefoge
    nick = welcome
    start nick
end