GS_Sell_Error

03:48:21 [INFO] Aus_Corza issued server command: /shop sell cobble 2
03:48:22 [SEVERE] null
org.bukkit.command.CommandException: Unhandled exception executing command 'shop' in plugin GiantShop v0.8.4.BETA
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:42)
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:168)
        at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:515)
        at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.java:880)
        at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:826)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:808)
        at org.getspout.spout.SpoutNetServerHandler.a(SpoutNetServerHandler.java:107)
        at net.minecraft.server.Packet3Chat.handle(Packet3Chat.java:44)
        at net.minecraft.server.NetworkManager.b(NetworkManager.java:292)
        at net.minecraft.server.NetServerHandler.d(NetServerHandler.java:109)
        at org.getspout.spout.SpoutNetServerHandler.d(SpoutNetServerHandler.java:173)
        at net.minecraft.server.ServerConnection.b(SourceFile:35)
        at net.minecraft.server.DedicatedServerConnection.b(SourceFile:30)
        at net.minecraft.server.MinecraftServer.q(MinecraftServer.java:580)
        at net.minecraft.server.DedicatedServer.q(DedicatedServer.java:213)
        at net.minecraft.server.MinecraftServer.p(MinecraftServer.java:476)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:407)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:539)
Caused by: java.lang.NumberFormatException: null
        at java.lang.Integer.parseInt(Integer.java:454)
        at java.lang.Integer.parseInt(Integer.java:527)
        at nl.giantit.minecraft.GiantShop.API.stock.core.itemStock.loadStock(itemStock.java:45)
        at nl.giantit.minecraft.GiantShop.API.stock.core.itemStock.<init>(itemStock.java:55)
        at nl.giantit.minecraft.GiantShop.API.stock.stockAPI.getItemStock(stockAPI.java:58)
        at nl.giantit.minecraft.GiantShop.core.Commands.chat.sell.sell(sell.java:217)
        at nl.giantit.minecraft.GiantShop.Executors.chat.exec(chat.java:61)
        at nl.giantit.minecraft.GiantShop.GiantShop.onCommand(GiantShop.java:160)
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:40)
        ... 17 more