Check for null in ItemStacks

src/main/java/com/sk89q/worldedit/bukkit/BukkitWorld.java

@@ -640,7 +640,7 @@ public class BukkitWorld extends LocalWorld {
 
         for (int i = 0; i < size; ++i) {
             ItemStack bukkitStack = inven.getItem(i);
-            if (bukkitStack.getTypeId() > 0) {
+            if (bukkitStack != null && bukkitStack.getTypeId() > 0) {
                 contents[i] = new BaseItemStack(
                         bukkitStack.getTypeId(),
                         bukkitStack.getAmount(),