Skript remove from inv error

[Skript] Severe Error:

If you're developing an add-on for Skript this likely means that you have done something wrong.
If you're a server admin however please go to http://dev.bukkit.org/server-mods/skript/tickets/
and check whether this error has already been reported.
If not please create a new ticket with a meaningful title, copy & paste this whole error into it,
and describe what you did before it happened and/or what you think caused the error.
If you think that it's a trigger that's causing the error please post the trigger as well.
By following this guide fixing the error should be easy and done fast.

Stack trace:
java.lang.NullPointerException
    at org.bukkit.craftbukkit.v1_7_R3.inventory.CraftInventory.getSize(CraftInventory.java:41)
    at org.bukkit.craftbukkit.v1_7_R3.inventory.CraftInventory.getContents(CraftInventory.java:54)
    at ch.njol.skript.aliases.ItemType.removeFrom(ItemType.java:771)
    at ch.njol.skript.classes.data.DefaultChangers$6.change(DefaultChangers.java:308)
    at ch.njol.skript.classes.data.DefaultChangers$6.change(DefaultChangers.java:1)
    at ch.njol.skript.classes.Changer$ChangerUtils.change(Changer.java:72)
    at ch.njol.skript.expressions.base.EventValueExpression.change(EventValueExpression.java:182)
    at ch.njol.skript.expressions.base.WrapperExpression.change(WrapperExpression.java:118)
    at ch.njol.skript.effects.EffChange.execute(EffChange.java:273)
    at ch.njol.skript.lang.Effect.run(Effect.java:50)
    at ch.njol.skript.lang.TriggerItem.walk(TriggerItem.java:63)
    at ch.njol.skript.lang.TriggerItem.walk(TriggerItem.java:91)
    at ch.njol.skript.effects.Delay$1.run(Delay.java:85)
    at org.bukkit.craftbukkit.v1_7_R3.scheduler.CraftTask.run(CraftTask.java:67)
    at org.bukkit.craftbukkit.v1_7_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:345)
    at net.minecraft.server.v1_7_R3.MinecraftServer.v(MinecraftServer.java:635)
    at net.minecraft.server.v1_7_R3.DedicatedServer.v(DedicatedServer.java:283)
    at net.minecraft.server.v1_7_R3.MinecraftServer.u(MinecraftServer.java:583)
    at net.minecraft.server.v1_7_R3.MinecraftServer.run(MinecraftServer.java:489)
    at net.minecraft.server.v1_7_R3.ThreadServerApplication.run(SourceFile:628)

Version Information:
  Skript: 2.1.2
  Bukkit: 1.7.9-R0.3-SNAPSHOT
  Minecraft: 1.7.9
  Java: 1.7.0

Running CraftBukkit: false

Current node: null
Current item: remove (event-item stack)->ch.njol.skript.aliases.ItemType from the block

Thread: Server thread

End of Error.