Code Error

class Game_Battler < Game_BattlerBase

  # Maximum number of monster zones and spell/trap zones
  MAX_MONSTER_ZONES = 3
  MAX_SPELL_TRAP_ZONES = 3

  def initialize
    @field = []
    @hand = []
    @monster_zones = Array.new(MAX_MONSTER_ZONES)
    @spell_trap_zones = Array.new(MAX_SPELL_TRAP_ZONES)
    super
  end

  # Returns the number of available monster zones
  def available_monster_zones
    @monster_zones.count(nil)
  end

  # Returns the number of available spell/trap zones
  def available_spell_trap_zones
    @spell_trap_zones.count(nil)
  end

  # Places a card from the hand into a monster zone
  def place_monster_card(card, zone_index)
    if zone_index >= MAX_MONSTER_ZONES || @monster_zones[zone_index]
      return false
    end

    @hand.delete(card)
    @monster_zones[zone_index] = card
    return true
  end

  # Places a card from the hand into a spell/trap zone
  def place_spell_trap_card(card, zone_index)
    if zone_index >= MAX_SPELL_TRAP_ZONES || @spell_trap_zones[zone_index]
      return false
    end

    @hand.delete(card)
    @spell_trap_zones[zone_index] = card
    return true
  end

  # Activates a spell card in a spell/trap zone
  def activate_spell_card(zone_index)
    card = @spell_trap_zones[zone_index]
    if !card || card.card_type != :spell
      return false
    end

    # Add logic for spell card effects
    @spell_trap_zones[zone_index] = nil
    return true
  end

  # Sets a trap card in a spell/trap zone
  def set_trap_card(card, zone_index)
    if zone_index >= MAX_SPELL_TRAP_ZONES || @spell_trap_zones[zone_index]
      return false
    end

    @hand.delete(card)
    @spell_trap_zones[zone_index] = card
    card.face_down = true
    return true
  end

  # Activates a trap card in a spell/trap zone
  def activate_trap_card(zone_index)
    card = @spell_trap_zones[zone_index]
    if !card || card.card_type != :trap || !card.face_down
      return false
    end

    # Add logic for trap card effects
    @spell_trap_zones[zone_index] = nil
    return true
  end