Do not serialize itemstack if air or amount 0

src/main/java/com/onarandombox/multiverseinventories/share/InventorySerializer.java

@@ -32,7 +32,7 @@ public Object serialize(ItemStack[] itemStacks) {
     private Map<String, ItemStack> mapSlots(ItemStack[] itemStacks) {
         Map<String, ItemStack> result = new HashMap<>(itemStacks.length);
         for (int i = 0; i < itemStacks.length; i++) {
-            if (itemStacks[i] != null && itemStacks[i].getType() != Material.AIR) {
+            if (itemStacks[i] != null && itemStacks[i].getType() != Material.AIR && itemStacks[i].getAmount() > 0) {
                 result.put(Integer.toString(i), itemStacks[i]);
             }
         }

src/main/java/com/onarandombox/multiverseinventories/share/ItemStackSerializer.java

@@ -0,0 +1,19 @@
+package com.onarandombox.multiverseinventories.share;
+
+import org.bukkit.Material;
+import org.bukkit.inventory.ItemStack;
+
+public class ItemStackSerializer implements SharableSerializer<ItemStack> {
+    @Override
+    public ItemStack deserialize(Object obj) {
+        return obj instanceof ItemStack ? (ItemStack) obj : null;
+    }
+
+    @Override
+    public Object serialize(ItemStack itemStack) {
+        if (itemStack == null || itemStack.getType() == Material.AIR || itemStack.getAmount() == 0) {
+            return null;
+        }
+        return itemStack;
+    }
+}

src/main/java/com/onarandombox/multiverseinventories/share/Sharables.java

@@ -148,7 +148,7 @@ public boolean updatePlayer(Player player, PlayerProfile profile) {
                     return true;
                 }
             }).serializer(new ProfileEntry(false, DataStrings.PLAYER_OFF_HAND_ITEM),
-                    new DefaultSerializer<>(ItemStack.class)).altName("shield").build();
+                    new ItemStackSerializer()).altName("shield").build();
 
     /**
      * Sharing Health.