SPIGOT-2787: Keep performing getter null conversion at call sites

src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java

@@ -220,6 +220,10 @@ public class CraftEventFactory {
         }
         BlockFace blockFace = CraftBlock.notchToBlockFace(direction);
 
+        if (itemInHand.getType() == Material.AIR || itemInHand.getAmount() == 0) {
+            itemInHand = null;
+        }
+
         PlayerInteractEvent event = new PlayerInteractEvent(player, action, itemInHand, blockClicked, blockFace, (hand == null) ? null : ((hand == EnumHand.OFF_HAND) ? EquipmentSlot.OFF_HAND : EquipmentSlot.HAND));
         if (cancelledBlock) {
             event.setUseInteractedBlock(Event.Result.DENY);
@@ -992,7 +996,7 @@ public class CraftEventFactory {
     }
 
     public static PrepareAnvilEvent callPrepareAnvilEvent(InventoryView view, ItemStack item) {
-        PrepareAnvilEvent event = new PrepareAnvilEvent(view, CraftItemStack.asCraftMirror(item));
+        PrepareAnvilEvent event = new PrepareAnvilEvent(view, CraftItemStack.asCraftMirror(item).clone());
         event.getView().getPlayer().getServer().getPluginManager().callEvent(event);
         event.getInventory().setItem(2, event.getResult());
         return event;
@@ -1012,7 +1016,7 @@ public class CraftEventFactory {
 
     public static EntityBreedEvent callEntityBreedEvent(EntityLiving child, EntityLiving mother, EntityLiving father, EntityLiving breeder, ItemStack bredWith, int experience) {
         org.bukkit.entity.LivingEntity breederEntity = (LivingEntity)(breeder == null ? null : breeder.getBukkitEntity());
-        CraftItemStack bredWithStack = CraftItemStack.asCraftMirror(bredWith);
+        CraftItemStack bredWithStack = bredWith == null ? null : CraftItemStack.asCraftMirror(bredWith).clone();
 
         EntityBreedEvent event = new EntityBreedEvent((LivingEntity) child.getBukkitEntity(), (LivingEntity) mother.getBukkitEntity(), (LivingEntity) father.getBukkitEntity(), breederEntity, bredWithStack, experience);
         child.world.getServer().getPluginManager().callEvent(event);

src/main/java/org/bukkit/craftbukkit/inventory/CraftInventory.java

@@ -46,7 +46,7 @@ public class CraftInventory implements Inventory {
 
     public ItemStack getItem(int index) {
         net.minecraft.server.ItemStack item = getInventory().getItem(index);
-        return CraftItemStack.asCraftMirror(item);
+        return item.isEmpty() ? null : CraftItemStack.asCraftMirror(item);
     }
 
     @Override
@@ -65,7 +65,7 @@ public class CraftInventory implements Inventory {
 
         int size = Math.min(items.length, mcItems.size());
         for (int i = 0; i < size; i++) {
-            items[i] = CraftItemStack.asCraftMirror(mcItems.get(i));
+            items[i] = (mcItems.get(i).isEmpty()) ? null : CraftItemStack.asCraftMirror(mcItems.get(i));
         }
         return items;
     }

src/main/java/org/bukkit/craftbukkit/inventory/CraftInventoryAnvil.java

@@ -28,10 +28,10 @@ public class CraftInventoryAnvil extends CraftInventory implements AnvilInventor
     public ItemStack getItem(int slot) {
         if (slot < getIngredientsInventory().getSize()) {
             net.minecraft.server.ItemStack item = getIngredientsInventory().getItem(slot);
-            return CraftItemStack.asCraftMirror(item);
+            return item.isEmpty() ? null : CraftItemStack.asCraftMirror(item);
         } else {
             net.minecraft.server.ItemStack item = getResultInventory().getItem(slot - getIngredientsInventory().getSize());
-            return CraftItemStack.asCraftMirror(item);
+            return item.isEmpty() ? null : CraftItemStack.asCraftMirror(item);
         }
     }
 

src/main/java/org/bukkit/craftbukkit/inventory/CraftInventoryCrafting.java

@@ -70,10 +70,10 @@ public class CraftInventoryCrafting extends CraftInventory implements CraftingIn
     public CraftItemStack getItem(int index) {
         if (index < getResultInventory().getSize()) {
             net.minecraft.server.ItemStack item = getResultInventory().getItem(index);
-            return CraftItemStack.asCraftMirror(item);
+            return item.isEmpty() ? null : CraftItemStack.asCraftMirror(item);
         } else {
             net.minecraft.server.ItemStack item = getMatrixInventory().getItem(index - getResultInventory().getSize());
-            return CraftItemStack.asCraftMirror(item);
+            return item.isEmpty() ? null : CraftItemStack.asCraftMirror(item);
         }
     }
 
@@ -99,7 +99,8 @@ public class CraftInventoryCrafting extends CraftInventory implements CraftingIn
 
     public ItemStack getResult() {
         net.minecraft.server.ItemStack item = getResultInventory().getItem(0);
-        return CraftItemStack.asCraftMirror(item);
+        if (!item.isEmpty()) return CraftItemStack.asCraftMirror(item);
+        return null;
     }
 
     public void setMatrix(ItemStack[] contents) {

src/main/java/org/bukkit/craftbukkit/inventory/CraftItemStack.java

@@ -68,7 +68,7 @@ public final class CraftItemStack extends ItemStack {
     }
 
     public static CraftItemStack asCraftMirror(net.minecraft.server.ItemStack original) {
-        return (original.isEmpty()) ? null : new CraftItemStack(original);
+        return new CraftItemStack(original);
     }
 
     public static CraftItemStack asCraftCopy(ItemStack original) {

src/test/java/org/bukkit/craftbukkit/inventory/NMSCraftItemStackTest.java

@@ -25,4 +25,12 @@ public class NMSCraftItemStackTest extends AbstractTestingBase {
         assertThat(clone.getData(), is(itemStack.getData()));
         assertThat(clone, is(itemStack));
     }
+
+    @Test
+    public void testCloneNullItem() throws Exception {
+        net.minecraft.server.ItemStack nmsItemStack = null;
+        ItemStack itemStack = CraftItemStack.asCraftMirror(nmsItemStack);
+        ItemStack clone = itemStack.clone();
+        assertThat(clone, is(itemStack));
+    }
 }