Handle empty items in pre 1.20.5 protocols

Maps empty items to null on read in 1.13, 1.13.2 and 1.20.2 item types and handles the empty item->null transition in 1.10->1.11

api/src/main/java/com/viaversion/viaversion/api/type/types/item/ItemType1_13.java

@@ -44,13 +44,16 @@ public class ItemType1_13 extends Type<Item> {
             item.setIdentifier(id);
             item.setAmount(buffer.readByte());
             item.setTag(Types.NAMED_COMPOUND_TAG.read(buffer));
+            if (item.isEmpty()) {
+                return null;
+            }
             return item;
         }
     }
 
     @Override
     public void write(ByteBuf buffer, @Nullable Item object) {
-        if (object == null) {
+        if (object == null || object.isEmpty()) {
             buffer.writeShort(-1);
         } else {
             buffer.writeShort(object.identifier());

api/src/main/java/com/viaversion/viaversion/api/type/types/item/ItemType1_13_2.java

@@ -44,13 +44,16 @@ public class ItemType1_13_2 extends Type<Item> {
             item.setIdentifier(Types.VAR_INT.readPrimitive(buffer));
             item.setAmount(buffer.readByte());
             item.setTag(Types.NAMED_COMPOUND_TAG.read(buffer));
+            if (item.isEmpty()) {
+                return null;
+            }
             return item;
         }
     }
 
     @Override
     public void write(ByteBuf buffer, @Nullable Item object) {
-        if (object == null) {
+        if (object == null || object.isEmpty()) {
             buffer.writeBoolean(false);
         } else {
             buffer.writeBoolean(true);

api/src/main/java/com/viaversion/viaversion/api/type/types/item/ItemType1_20_2.java

@@ -45,12 +45,15 @@ public class ItemType1_20_2 extends Type<Item> {
         item.setIdentifier(Types.VAR_INT.readPrimitive(buffer));
         item.setAmount(buffer.readByte());
         item.setTag(Types.COMPOUND_TAG.read(buffer));
+        if (item.isEmpty()) {
+            return null;
+        }
         return item;
     }
 
     @Override
     public void write(final ByteBuf buffer, @Nullable final Item object) {
-        if (object == null) {
+        if (object == null || object.isEmpty()) {
             buffer.writeBoolean(false);
         } else {
             buffer.writeBoolean(true);

common/src/main/java/com/viaversion/viaversion/protocols/v1_10to1_11/rewriter/ItemPacketRewriter1_11.java

@@ -74,6 +74,10 @@ public class ItemPacketRewriter1_11 extends ItemRewriter<ClientboundPackets1_9_3
 
     @Override
     public Item handleItemToClient(UserConnection connection, Item item) {
+        if (item != null && item.isEmpty()) {
+            // Map empty items to null
+            return null;
+        }
         EntityMappings1_11.toClientItem(item);
         return item;
     }

common/src/main/java/com/viaversion/viaversion/protocols/v1_20_3to1_20_5/rewriter/BlockItemPacketRewriter1_20_5.java

@@ -355,12 +355,7 @@ public final class BlockItemPacketRewriter1_20_5 extends ItemRewriter<Clientboun
     }
 
     @Override
-    public Item handleItemToClient(final UserConnection connection, @Nullable final Item item) {
-        if (item == null) {
-            // We no longer want null items, always unify them to empty
-            return StructuredItem.empty();
-        }
-
+    public Item handleItemToClient(final UserConnection connection, final Item item) {
         // Add the original as custom data, to be re-used for creative clients as well
         final CompoundTag tag = item.tag();
         if (tag != null) {
@@ -380,12 +375,7 @@ public final class BlockItemPacketRewriter1_20_5 extends ItemRewriter<Clientboun
     }
 
     @Override
-    public @Nullable Item handleItemToServer(UserConnection connection, final Item item) {
-        if (item.isEmpty()) {
-            // Empty to null for the old protocols
-            return null;
-        }
-
+    public Item handleItemToServer(UserConnection connection, final Item item) {
         super.handleItemToServer(connection, item);
         return toOldItem(connection, item, DATA_CONVERTER);
     }