SPIGOT-4576: Fix attributes in itemstack internal data being lost

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

@@ -111,6 +111,8 @@ public class CraftMetaBlockState extends CraftMetaItem implements BlockStateMeta
 
     @Override
     void deserializeInternal(NBTTagCompound tag, Object context) {
+        super.deserializeInternal(tag, context);
+
         if (tag.hasKeyOfType(BLOCK_ENTITY_TAG.NBT, CraftMagicNumbers.NBT.TAG_COMPOUND)) {
             blockEntityTag = tag.getCompound(BLOCK_ENTITY_TAG.NBT);
         }

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

@@ -385,7 +385,7 @@ class CraftMetaItem implements ItemMeta, Damageable, Repairable {
 
     static Multimap<Attribute, AttributeModifier> buildModifiers(NBTTagCompound tag, ItemMetaKey key) {
         Multimap<Attribute, AttributeModifier> modifiers = HashMultimap.create();
-        if (!tag.hasKey(key.NBT)) {
+        if (!tag.hasKeyOfType(key.NBT, CraftMagicNumbers.NBT.TAG_LIST)) {
             return modifiers;
         }
         NBTTagList mods = tag.getList(key.NBT, CraftMagicNumbers.NBT.TAG_COMPOUND);
@@ -504,6 +504,10 @@ class CraftMetaItem implements ItemMeta, Damageable, Repairable {
     }
 
     void deserializeInternal(NBTTagCompound tag, Object context) {
+        // SPIGOT-4576: Need to migrate from internal to proper data
+        if (tag.hasKeyOfType(ATTRIBUTES.NBT, CraftMagicNumbers.NBT.TAG_LIST)) {
+            this.attributeModifiers = buildModifiers(tag, ATTRIBUTES);
+        }
     }
 
     static Map<Enchantment, Integer> buildEnchantments(Map<String, Object> map, ItemMetaKey key) {

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

@@ -58,6 +58,8 @@ class CraftMetaSkull extends CraftMetaItem implements SkullMeta {
 
     @Override
     void deserializeInternal(NBTTagCompound tag, Object context) {
+        super.deserializeInternal(tag, context);
+
         if (tag.hasKeyOfType(SKULL_PROFILE.NBT, CraftMagicNumbers.NBT.TAG_COMPOUND)) {
             profile = GameProfileSerializer.deserialize(tag.getCompound(SKULL_PROFILE.NBT));
         }