diff --git a/src/Luban.Job.Common/Source/TypeVisitors/CsSerializeVisitor.cs b/src/Luban.Job.Common/Source/TypeVisitors/CsSerializeVisitor.cs
index dae970f..0fcada8 100644
--- a/src/Luban.Job.Common/Source/TypeVisitors/CsSerializeVisitor.cs
+++ b/src/Luban.Job.Common/Source/TypeVisitors/CsSerializeVisitor.cs
@@ -10,17 +10,12 @@ namespace Luban.Job.Common.TypeVisitors
         {
             if (type.IsNullable)
             {
-                return $"if({fieldName} != null){{ {bufName}.WriteBool(true); {type.Apply(CsUnderingSerializeVisitor.Ins, bufName, type.Apply(CsIsRawNullableTypeVisitor.Ins) ? fieldName : fieldName + ".Value" )} }} else {{ {bufName}.WriteBool(true); }}";
+                return $"{{ if({fieldName} is {type.Apply(CsUnderingDefineTypeName.Ins)} __value__){{ {bufName}.WriteBool(true); {type.Apply(CsUnderingSerializeVisitor.Ins, bufName, "__value__" )} }} else {{ {bufName}.WriteBool(false); }} }}";
             }
             else
             {
                 return type.Apply(CsUnderingSerializeVisitor.Ins, bufName, fieldName);
             }
         }
-
-        public override string Accept(TBean type, string bufName, string fieldName)
-        {
-            return type.Apply(CsUnderingSerializeVisitor.Ins, bufName, fieldName);
-        }
     }
 }
diff --git a/src/Luban.Server/Templates/proto/cs/bean.tpl b/src/Luban.Server/Templates/proto/cs/bean.tpl
index 1e3006a..20275fc 100644
--- a/src/Luban.Server/Templates/proto/cs/bean.tpl
+++ b/src/Luban.Server/Templates/proto/cs/bean.tpl
@@ -40,15 +40,8 @@ namespace {{x.namespace_with_top_module}}
         public static void Serialize{{name}}(ByteBuf _buf, {{name}} x)
         {
     {{~if is_abstract_type~}}
-            if (x != null)
-            {
-                _buf.WriteInt(x.GetTypeId());
-                x.Serialize(_buf);
-            }
-            else
-            {
-                _buf.WriteInt(0);
-            }
+            _buf.WriteInt(x.GetTypeId());
+            x.Serialize(_buf);
     {{~else~}}
             x.Serialize(_buf);
     {{~end~}}
@@ -60,7 +53,6 @@ namespace {{x.namespace_with_top_module}}
            {{full_name}} x;
             switch (_buf.ReadInt())
             {
-                case 0 : return null;
             {{~ for child in x.hierarchy_not_abstract_children~}}
                 case {{child.full_name}}.__ID__: x = new {{child.full_name}}(); break;
             {{~end~}}