Remove null values in TileEntity tick list

Because who wouldn't want to tick a null tile entity right?
Fixes GH-851

Spigot-API-Patches/0006-Add-async-chunk-load-API.patch

@@ -1,17 +1,18 @@
-From 8793e6a8cbd642c7d5c8e0572888eea9df36e247 Mon Sep 17 00:00:00 2001
+From 0cbfecff228b4248ddff45b9774891905cf2bf4a Mon Sep 17 00:00:00 2001
 From: Aikar <aikar@aikar.co>
 Date: Mon, 29 Feb 2016 17:43:33 -0600
 Subject: [PATCH] Add async chunk load API
 
 
 diff --git a/src/main/java/org/bukkit/World.java b/src/main/java/org/bukkit/World.java
-index e9b1b0a..56f5029 100644
+index 67b0d516..21b2733f 100644
 --- a/src/main/java/org/bukkit/World.java
 +++ b/src/main/java/org/bukkit/World.java
-@@ -137,6 +137,78 @@ public interface World extends PluginMessageRecipient, Metadatable {
+@@ -136,6 +136,78 @@ public interface World extends PluginMessageRecipient, Metadatable {
+      */
      public Chunk getChunkAt(Block block);
  
-     /**
++    /**
 +     * Used by {@link World#getChunkAtAsync(Location,ChunkLoadCallback)} methods
 +     * to request a {@link Chunk} to be loaded, with this callback receiving
 +     * the chunk when it is finished.
@@ -83,10 +84,9 @@ index e9b1b0a..56f5029 100644
 +     */
 +    public void getChunkAtAsync(Block block, ChunkLoadCallback cb);
 +
-+    /**
+     /**
       * Checks if the specified {@link Chunk} is loaded
       *
-      * @param chunk The chunk to check
 -- 
-2.9.3
+2.14.1