[Error] Why is my Weather code causing crashes upon the use of some random moves when weather is up?

[SuperSpyroDragon64]

If a weather condition like Sun or Hail is active, all moves have a small chance to cause crashes inconsistently. The error messages claim * is undefined. Sometimes moves work and, if weather effects are active, sometimes they crash. If it was a specific move I'd know what move to look at, but I think my Weather code is the problem.

    # Weather
    case @battle.pbWeather
    when :Sun, :HarshSun
      if type == :FIRE
        multipliers[:final_damage_multiplier] *= 2 if !target.hasUtilityUmbrella?
      elsif type == :GRASS
        multipliers[:final_damage_multiplier] *= 2 if !target.hasUtilityUmbrella?
      elsif type == :WATER
        multipliers[:final_damage_multiplier] /= 2 if !target.hasUtilityUmbrella?
      end
            if target.pbHasType?(:FIRE)
        multipliers[:defense_multiplier] *= 2
        multipliers[:special_defense_multiplier] *= 2
      end
                  if target.pbHasType?(:GRASS)
        multipliers[:defense_multiplier] *= 2
        multipliers[:special_defense_multiplier] *= 2
        end
          when :Hail
      if type == :FIRE
        multipliers[:final_damage_multiplier] /= 2 if !target.hasUtilityUmbrella?
      elsif type == :ICE
        multipliers[:final_damage_multiplier] *= 2.5 if !target.hasUtilityUmbrella?
      end
            if target.pbHasType?(:ICE)
        multipliers[:defense_multiplier] *= 2.5
        multipliers[:special_defense_multiplier] *= 2.5
end
    when :Rain, :HeavyRain
      if type == :FIRE
        multipliers[:final_damage_multiplier] /= 2 if !target.hasUtilityUmbrella?
              elsif type == :ELECTRIC
        multipliers[:final_damage_multiplier] *= 2 if !target.hasUtilityUmbrella?
              elsif type == :GRASS
        multipliers[:final_damage_multiplier] *= 2 if !target.hasUtilityUmbrella?
      elsif type == :WATER
        multipliers[:final_damage_multiplier] *= 2 if !target.hasUtilityUmbrella?
      end
                        if target.pbHasType?(:WATER)
        multipliers[:defense_multiplier] *= 2
        multipliers[:special_defense_multiplier] *= 2
      end
                        if target.pbHasType?(:ELECTRIC)
        multipliers[:defense_multiplier] *= 2
        multipliers[:special_defense_multiplier] *= 2
      end
                        if target.pbHasType?(:GRASS)
        multipliers[:defense_multiplier] *= 2
        multipliers[:special_defense_multiplier] *= 2
        end
    when :Sandstorm
           if type == :GROUND
        multipliers[:final_damage_multiplier] *= 2 if !target.hasUtilityUmbrella?
              elsif type == :ROCK
        multipliers[:final_damage_multiplier] *= 2 if !target.hasUtilityUmbrella?
              elsif type == :STEEL
        multipliers[:final_damage_multiplier] *= 1.5 if !target.hasUtilityUmbrella?
        end
      if target.pbHasType?(:ROCK)
        multipliers[:defense_multiplier] *= 2
      if target.pbHasType?(:GROUND)
        multipliers[:defense_multiplier] *= 2
              if target.pbHasType?(:STEEL)
        multipliers[:defense_multiplier] *= 1.5
      end
      end
    end
  end