From a3c6e44b68c4493d0c366bee0dcc6aeec4873dd4 Mon Sep 17 00:00:00 2001
From: dalizi2333 <dalizi233@qq.com>
Date: Wed, 17 Jun 2026 05:04:49 +0800
Subject: [PATCH] Fixed cover removal not syncing render state to clients

- SyncDataHolder.serializeField: removed the !isSyncManaged condition from null check so that nullable ISyncManaged fields (e.g. CoverBehavior) are properly serialized as null instead of being silently skipped, causing client-side render desync when a cover is removed.

- CoverBehaviorTransformer: serializeNBT now returns null tag for null values instead of an empty tag; deserializeNBT now handles null tag as a defensive measure.
---
 .../gregtechceu/gtceu/api/sync_system/SyncDataHolder.java  | 2 +-
 .../data_transformers/gtceu/CoverBehaviorTransformer.java  | 7 ++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/main/java/com/gregtechceu/gtceu/api/sync_system/SyncDataHolder.java b/src/main/java/com/gregtechceu/gtceu/api/sync_system/SyncDataHolder.java
index eb9ff723d36..6d97b08ac94 100644
--- a/src/main/java/com/gregtechceu/gtceu/api/sync_system/SyncDataHolder.java
+++ b/src/main/java/com/gregtechceu/gtceu/api/sync_system/SyncDataHolder.java
@@ -105,7 +105,7 @@ private static Tag serializeField(HolderLookup.Provider registries, ISyncManaged
                                       boolean writeClientFields, boolean fullSync) {
         Object currentValue = field.handle.get(holder);
 
-        if (!field.isSyncManaged && currentValue == null) {
+        if (currentValue == null) {
             var nullCompound = new CompoundTag();
             nullCompound.putBoolean("null", true);
             return nullCompound;
diff --git a/src/main/java/com/gregtechceu/gtceu/api/sync_system/data_transformers/gtceu/CoverBehaviorTransformer.java b/src/main/java/com/gregtechceu/gtceu/api/sync_system/data_transformers/gtceu/CoverBehaviorTransformer.java
index f3fcc94e200..78a4c2c6e90 100644
--- a/src/main/java/com/gregtechceu/gtceu/api/sync_system/data_transformers/gtceu/CoverBehaviorTransformer.java
+++ b/src/main/java/com/gregtechceu/gtceu/api/sync_system/data_transformers/gtceu/CoverBehaviorTransformer.java
@@ -23,13 +23,18 @@ public Tag serializeNBT(@Nullable CoverBehavior value,
         if (value != null) {
             return serialize(value, context.isClientSync(), context.lookup());
         }
-        return new CompoundTag();
+        var nullTag = new CompoundTag();
+        nullTag.putBoolean("null", true);
+        return nullTag;
     }
 
     @Override
     public @Nullable CoverBehavior deserializeNBT(Tag tag,
                                                   CoverBehaviorTransformer.TransformerContext<CoverBehavior> context) {
         var compoundTag = ValueTransformer.assertTagType(CompoundTag.class, tag, context);
+        if (compoundTag.getBoolean("null")) {
+            return null;
+        }
         if (context.holder() instanceof ICoverable coverable) {
             return deserialize(compoundTag, coverable, context.currentValue(), context.isClientSync(),
                     context.lookup());