EntityInfo - Stack Trace

org.bukkit.command.CommandException: Unhandled exception executing command 'ei' in plugin EntityInfo v0.0.0
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:175) ~[spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at org.bukkit.craftbukkit.v1_7_R1.CraftServer.dispatchCommand(CraftServer.java:706) ~[spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.PlayerConnection.handleCommand(PlayerConnection.java:984) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.PlayerConnection.a(PlayerConnection.java:829) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.PacketPlayInChat.a(PacketPlayInChat.java:28) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.PacketPlayInChat.handle(PacketPlayInChat.java:65) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.NetworkManager.a(NetworkManager.java:147) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.ServerConnection.c(ServerConnection.java:77) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.MinecraftServer.u(MinecraftServer.java:700) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.DedicatedServer.u(DedicatedServer.java:273) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.MinecraftServer.t(MinecraftServer.java:562) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.MinecraftServer.run(MinecraftServer.java:469) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        at net.minecraft.server.v1_7_R1.ThreadServerApplication.run(SourceFile:617) [spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
Caused by: java.lang.UnsupportedOperationException
        at java.util.AbstractList.remove(AbstractList.java:161) ~[?:1.7.0_45]
        at org.minecraftsmp.entityinfo.EntityInfo.onCommand(EntityInfo.java:77) ~[?:?] << Most interesting line
        at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[spigot.jar:git-Spigot-1.7.2-R0.3-122-gb58e277]
        ... 13 more