Development Assistance Block Health Problem

I have code like this for my Power Stone plugin

Code:

    @EventHandler
    public void tb(final PlayerInteractEvent event){
        Player player = (Player)event.getPlayer();
        Arena arena = plugin.getArena(plugin.psap.get(player.getName()));
        for(final String pla : arena.getPlayers()){
        ItemStack item = player.getItemInHand();
        int red = (int)plugin.block.get(arena.getName()+"RED");
        int blue = (int)plugin.block.get(arena.getName()+"BLUE");
        if(event.getAction() == Action.LEFT_CLICK_BLOCK){
            Block block = event.getClickedBlock();
           
            if(block.getType() == Material.REDSTONE_BLOCK){
                if(plugin.getColor(player) == ChatColor.RED){
                    event.setCancelled(true);
                    return;
                }
                if(plugin.getColor(player) == ChatColor.BLUE){
                if(item.getType() == Material.DIAMOND_PICKAXE){
                if(red >= 1){
                    plugin.block.put(arena.getName()+"RED", red - 1);
                    Bukkit.getPlayer(pla).sendMessage(plugin.ps+"RED TEAM POWER STONE LIFES : " + red);
                    event.setCancelled(true);
                }
                if(red == 0){
                this.plugin.getServer().broadcastMessage(ChatColor.GOLD+"[POWERSTONE] BLUE TEAM HAS WIN POWERSTONE GAME ON ARENA "+arena.getName().toUpperCase());
                this.plugin.endArena(arena.getName());
                block.breakNaturally();
                }
                }
                }
            }
            if(block.getType() == Material.LAPIS_BLOCK){
                if(plugin.getColor(player) == ChatColor.BLUE){
                    event.setCancelled(true);
                    return;
                }
                if(plugin.getColor(player) == ChatColor.RED){
                if(item.getType() == Material.DIAMOND_PICKAXE){
                if(blue >= 1){
                    plugin.block.put(arena.getName()+"BLUE", blue - 1);
                    Bukkit.getPlayer(pla).sendMessage(plugin.ps+"BLUE TEAM POWER STONE LIFES : " + blue);
                    event.setCancelled(true);
                }
                if(blue == 0){
                this.plugin.getServer().broadcastMessage(ChatColor.GOLD+"[POWERSTONE] RED TEAM HAS WIN POWERSTONE GAME ON ARENA "+arena.getName().toUpperCase());
                this.plugin.endArena(arena.getName());
                block.breakNaturally();
                }
                }
                }
            }
        }
    }
    }

But when i test the code. console send error like this

Code:

26.01 06:03:02 [Server] INFO ... 15 more
26.01 06:03:02 [Server] INFO at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:298) ~[Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.7.0_72]
26.01 06:03:02 [Server] INFO at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.7.0_72]
26.01 06:03:02 [Server] INFO at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.7.0_72]
26.01 06:03:02 [Server] INFO at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.7.0_72]
26.01 06:03:02 [Server] INFO at samuel81.ps.listener.tb(listener.java:122) ~[?:?]
26.01 06:03:02 [Server] INFO at java.util.ArrayList$Itr.next(Unknown Source) ~[?:1.7.0_72]
26.01 06:03:02 [Server] INFO at java.util.ArrayList$Itr.checkForComodification(Unknown Source) ~[?:1.7.0_72]
26.01 06:03:02 [Server] INFO Caused by: java.util.ConcurrentModificationException
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.ThreadServerApplication.run(SourceFile:628) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.MinecraftServer.run(MinecraftServer.java:490) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.MinecraftServer.u(MinecraftServer.java:584) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.DedicatedServer.v(DedicatedServer.java:289) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.MinecraftServer.v(MinecraftServer.java:734) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.ServerConnection.c(ServerConnection.java:81) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.NetworkManager.a(NetworkManager.java:186) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.PacketPlayInBlockDig.handle(PacketPlayInBlockDig.java:65) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.PacketPlayInBlockDig.a(PacketPlayInBlockDig.java:41) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.PlayerConnection.a(PlayerConnection.java:552) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at net.minecraft.server.v1_7_R4.PlayerInteractManager.dig(PlayerInteractManager.java:103) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at org.bukkit.craftbukkit.v1_7_R4.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:242) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:494) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:509) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302) ~[Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:03:02 [Server] INFO org.bukkit.event.EventException
26.01 06:03:02 [Server] ERROR Could not pass event PlayerInteractEvent to PowerStone v0.1
26.01 06:03:02 [Server] INFO BLUE TEAM HAS WIN POWERSTONE GAME ON ARENA TEST
26.01 06:02:04 [Server] INFO ... 15 more
26.01 06:02:04 [Server] INFO at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:298) ~[Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at java.lang.reflect.Method.invoke(Unknown Source) ~[?:1.7.0_72]
26.01 06:02:04 [Server] INFO at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:1.7.0_72]
26.01 06:02:04 [Server] INFO at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:1.7.0_72]
26.01 06:02:04 [Server] INFO at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.7.0_72]
26.01 06:02:04 [Server] INFO at samuel81.ps.listener.tb(listener.java:124) ~[?:?]
26.01 06:02:04 [Server] INFO Caused by: java.lang.NullPointerException
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.ThreadServerApplication.run(SourceFile:628) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.MinecraftServer.run(MinecraftServer.java:490) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.MinecraftServer.u(MinecraftServer.java:584) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.DedicatedServer.v(DedicatedServer.java:289) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.MinecraftServer.v(MinecraftServer.java:734) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.ServerConnection.c(ServerConnection.java:81) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.NetworkManager.a(NetworkManager.java:186) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.PacketPlayInBlockDig.handle(PacketPlayInBlockDig.java:65) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.PacketPlayInBlockDig.a(PacketPlayInBlockDig.java:41) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.PlayerConnection.a(PlayerConnection.java:552) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at net.minecraft.server.v1_7_R4.PlayerInteractManager.dig(PlayerInteractManager.java:103) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at org.bukkit.craftbukkit.v1_7_R4.event.CraftEventFactory.callPlayerInteractEvent(CraftEventFactory.java:242) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:494) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:509) [Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:302) ~[Spigot.jar:git-Spigot-1.7.9-R0.2-208-ge0f2e95]
26.01 06:02:04 [Server] INFO org.bukkit.event.EventException
26.01 06:02:04 [Server] ERROR Could not pass event PlayerInteractEvent to PowerStone v0.1

 

You have a null at line 124.