[Server thread/WARN] [opencomputers]: Unexpected error in Lua callback. java.lang.NullPointerException: null	at net.minecraft.item.ItemStack.func_77989_b(ItemStack.java:432) ~[aip.class:?]	at li.cil.oc.server.agent.Player.callUsingItemInSlot(Player.scala:507) ~[Player.class:?]	at li.cil.oc.server.agent.Player.clickBlock(Player.scala:360) ~[Player.class:?]	at li.cil.oc.server.component.Agent$class.click$1(Agent.scala:113) ~[Agent$class.class:?]	at li.cil.oc.server.component.Agent$$anonfun$swing$1.apply(Agent.scala:135) ~[Agent$$anonfun$swing$1.class:?]	at li.cil.oc.server.component.Agent$$anonfun$swing$1.apply(Agent.scala:122) ~[Agent$$anonfun$swing$1.class:?]	at scala.collection.immutable.List.foreach(List.scala:383) ~[List.class:?]	at li.cil.oc.server.component.Agent$class.swing(Agent.scala:122) ~[Agent$class.class:?]	at li.cil.oc.server.component.Robot.swing(Robot.scala:32) ~[Robot.class:?]	at generated.li.cil.oc.CallWrapper_li_cil_oc_server_component_Robot_swing.call(Unknown Source) ~[?:?]	at li.cil.oc.server.machine.Callbacks$ComponentCallback.apply(Callbacks.scala:123) ~[Callbacks$ComponentCallback.class:?]	at li.cil.oc.server.network.Component$class.invoke(Component.scala:112) ~[Component$class.class:?]	at li.cil.oc.server.network.Network$ComponentConnectorBuilder$$anon$1.invoke(Network.scala:631) ~[Network$ComponentConnectorBuilder$$anon$1.class:?]	at li.cil.oc.server.machine.Machine.invoke(Machine.scala:360) ~[Machine.class:?]	at li.cil.oc.server.machine.luac.ComponentAPI$$anonfun$initialize$5$$anonfun$apply$6.apply(ComponentAPI.scala:78) ~[ComponentAPI$$anonfun$initialize$5$$anonfun$apply$6.class:?]	at li.cil.oc.server.machine.luac.ComponentAPI$$anonfun$initialize$5$$anonfun$apply$6.apply(ComponentAPI.scala:78) ~[ComponentAPI$$anonfun$initialize$5$$anonfun$apply$6.class:?]	at li.cil.oc.server.machine.luac.NativeLuaArchitecture.invoke(NativeLuaArchitecture.scala:55) [NativeLuaArchitecture.class:?]	at li.cil.oc.server.machine.luac.ComponentAPI$$anonfun$initialize$5.apply(ComponentAPI.scala:78) [ComponentAPI$$anonfun$initialize$5.class:?]	at li.cil.oc.server.machine.luac.ComponentAPI$$anonfun$initialize$5.apply(ComponentAPI.scala:74) [ComponentAPI$$anonfun$initialize$5.class:?]	at li.cil.oc.util.ExtendedLuaState$ExtendedLuaState$$anon$1.invoke(ExtendedLuaState.scala:24) [ExtendedLuaState$ExtendedLuaState$$anon$1.class:?]	at li.cil.repack.com.naef.jnlua.LuaStateFiveThree.lua_pcall(Native Method) ~[LuaStateFiveThree.class:?]	at li.cil.repack.com.naef.jnlua.LuaState.call(LuaState.java:681) [LuaState.class:?]	at li.cil.oc.server.machine.luac.NativeLuaArchitecture.runSynchronized(NativeLuaArchitecture.scala:177) [NativeLuaArchitecture.class:?]	at li.cil.oc.server.machine.Machine.update(Machine.scala:564) [Machine.class:?]	at li.cil.oc.common.EventHandler$$anonfun$onServerTick$2.apply(EventHandler.scala:168) [EventHandler$$anonfun$onServerTick$2.class:?]	at li.cil.oc.common.EventHandler$$anonfun$onServerTick$2.apply(EventHandler.scala:166) [EventHandler$$anonfun$onServerTick$2.class:?]	at scala.collection.mutable.HashSet.foreach(HashSet.scala:78) [scala-library-2.11.1.jar:?]	at li.cil.oc.common.EventHandler$.onServerTick(EventHandler.scala:166) [EventHandler$.class:?]	at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_1225_EventHandler$_onServerTick_ServerTickEvent.invoke(.dynamic) [?:?]	at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90) [ASMEventHandler.class:?]	at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:182) [EventBus.class:?]	at net.minecraftforge.fml.common.FMLCommonHandler.onPreServerTick(FMLCommonHandler.java:279) [FMLCommonHandler.class:?]	at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:657) [MinecraftServer.class:?]	at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:252) [chd.class:?]	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526) [MinecraftServer.class:?]	at java.lang.Thread.run(Thread.java:748) [?:1.8.0_161]