Bukkit

This error happens often, and I have not actually used the plugin yet.

[SEVERE] Could not pass event PlayerInteractEvent to Pushball
org.bukkit.event.EventException
    at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:303)
    at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
    at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:459)
    at org.bukkit.craftbukkit.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:176)
    at net.minecraft.server.ItemInWorldManager.dig(ItemInWorldManager.java:94)
    at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:537)
    at net.minecraft.server.Packet14BlockDig.handle(SourceFile:43)
    at net.minecraft.server.NetworkManager.b(NetworkManager.java:229)
    at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:113)
    at net.minecraft.server.NetworkListenThread.a(NetworkListenThread.java:78)
    at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:551)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:449)
    at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
Caused by: java.lang.NullPointerException