bukkit error

01:06:11 [SEVERE] Could not pass event PLAYER_INTERACT to SignShop
java.lang.NullPointerException
        at Ne0nx3r0.SignShop.SignShopPlayerListener.onPlayerInteract(SignShopPla
yerListener.java:310)
        at org.bukkit.plugin.java.JavaPluginLoader$10.execute(JavaPluginLoader.j
ava:306)
        at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.jav
a:58)
        at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.j
ava:310)
        at org.bukkit.craftbukkit.event.CraftEventFactory.callPlayerInteractEven
t(CraftEventFactory.java:166)
        at net.minecraft.server.ItemInWorldManager.dig(ItemInWorldManager.java:6
3)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:453)
        at net.minecraft.server.Packet14BlockDig.a(SourceFile:42)
        at net.minecraft.server.NetworkManager.b(NetworkManager.java:226)
        at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:75)
        at net.minecraft.server.NetworkListenThread.a(SourceFile:105)
        at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:399)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:309)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:422)