Cease execution if block is AIR. Fixes BUKKIT-2104

src/main/java/net/minecraft/server/ItemInWorldManager.java

@@ -271,6 +271,7 @@ public class ItemInWorldManager {
             return false;
         } else {
             int l = this.world.getTypeId(i, j, k);
+            if (Block.byId[l] == null) return false; // CraftBukkit - a plugin set block to air without cancelling
             int i1 = this.world.getData(i, j, k);
 
             this.world.a(this.player, 2001, i, j, k, l + (this.world.getData(i, j, k) << 12));

src/main/java/net/minecraft/server/PlayerInventory.java

@@ -363,12 +363,6 @@ public class PlayerInventory implements IInventory {
     }
 
     public boolean b(Block block) {
-        // CraftBukkit start - fixed NPE
-        if (block == null) {
-            return false;
-        }
-        // CraftBukkit end
-
         if (block.material.isAlwaysDestroyable()) {
             return true;
         } else {