Bow 50 level in enchant table

13:56:45 [WARNING] Failed to handle packet: java.lang.NullPointerException
java.lang.NullPointerException
        at net.minecraft.server.ContainerEnchantTable.a(ContainerEnchantTable.java:147)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:1008)
        at net.minecraft.server.Packet108ButtonClick.handle(SourceFile:18)
        at net.minecraft.server.NetworkManager.b(NetworkManager.java:226)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:100)
        at org.getspout.spout.SpoutNetServerHandler.a(SpoutNetServerHandler.java:552)
        at net.minecraft.server.NetworkListenThread.a(NetworkListenThread.java:78)
        at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:536)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:434)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)