Solved Problems with chests

I am having a problem with filling chests in my plugin. Everytime the plugin wants to fill all the chests in a certain arena it says the chests are not chests but CraftBlocks instead. As far as I know, all the chests set up are chests and while setting up the arenas it checks if the blocks saved are actually chests.

The stack trace:

Code:

java.lang.IllegalStateException: CraftChest is not a chest but is instead CraftB

lock{chunk=CraftChunk{x=-123z=-19},x=-1957,y=54,z=-302,type=CHEST,data=2}
        at org.bukkit.craftbukkit.v1_8_R3.block.CraftChest.getInventory(CraftChe
st.java:50) ~[testing_server.jar:git-Bukkit-18fbb24]
        at me.kahjiit.hungergames.Crate.fill(Crate.java:67) ~[?:?]
        at me.kahjiit.hungergames.Arena.fillCrates(Arena.java:88) ~[?:?]
        at me.kahjiit.hungergames.GameTimer$2.run(GameTimer.java:69) ~[?:?]
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java
:53) ~[testing_server.jar:git-Bukkit-18fbb24]
        at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftScheduler.mainThreadHea
rtbeat(CraftScheduler.java:349) [testing_server.jar:git-Bukkit-18fbb24]
        at net.minecraft.server.v1_8_R3.MinecraftServer.B(MinecraftServer.java:6
80) [testing_server.jar:git-Bukkit-18fbb24]
        at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:3
35) [testing_server.jar:git-Bukkit-18fbb24]
        at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:6
29) [testing_server.jar:git-Bukkit-18fbb24]
        at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java
:537) [testing_server.jar:git-Bukkit-18fbb24]
        at java.lang.Thread.run(Thread.java:745) [?:1.8.0_40]

fill() in Crate:

Code:

public void fill() {
        chest.getBlockInventory().clear();
       
        Map<Material, Integer> items1 = ItemManager.getInstance().getMaterialList(1);
        Map<Material, Integer> items2 = ItemManager.getInstance().getMaterialList(2);
       
        Random r = new Random();
       
        int numItems = r.nextInt(5) + 2;
       
        for (int i = 0; i < numItems; i++) {
            Material material = null;
            ItemStack item = null;
           
            if (tier == 1) {
                material = getRandomMaterial(items1);
                item = new ItemStack(material, getRandomAmount(material, 1));
            }
           
            if (tier == 2) {
                material = getRandomMaterial(items2);
                item = new ItemStack(material, getRandomAmount(material, 2));
            }
           
            if (item.getType() == Material.FLINT_AND_STEEL) {
                item.setDurability((short) 62);
            }
           
            int index;
           
            do {
                index = r.nextInt(chest.getInventory().getSize()); //Line 67
            } while (chest.getInventory().getItem(index) != null);
           
            chest.getInventory().setItem(index, item);
        }
    }

Additional chests loading:

Code:

public void loadCrates(Arena arena, Game game) {
        try {
            for (String num : sm.getArenaYaml().getConfigurationSection("arenas." + game.getID() + ".maps." + arena.getName() + ".chests").getKeys(false)) {
                Location loc = sm.getLocation("arenas." + game.getID() + ".maps." + arena.getName() + ".chests." + num);
                int tier = sm.getArenaYaml().getInt("arenas." + game.getID() + ".maps." + arena.getName() + ".chests." + num + ".tier");
               
                if (loc.getBlock().getState() instanceof Chest) {
                    Crate crate = new Crate((Chest) loc.getBlock().getState(), tier);
                   
                    arena.addCrate(crate);
                }
            }
        } catch (NullPointerException e) {
            logger.warning("[HungerGames] Cannot find any crates from arena " + arena.getName() + "!");
        }
    }

EDIT:
Using chest.getBlockInventory() instead of chest.getInventory() fixed the bug.