diff --git a/compiler/cpp/src/thrift/generate/t_netstd_generator.cc b/compiler/cpp/src/thrift/generate/t_netstd_generator.cc
index 0373faf..e9c579c 100644
--- a/compiler/cpp/src/thrift/generate/t_netstd_generator.cc
+++ b/compiler/cpp/src/thrift/generate/t_netstd_generator.cc
@@ -1173,17 +1173,8 @@
         t_type* ttype = (*m_iter)->get_type();
         string copy_op = get_deep_copy_method_call(ttype, needs_typecast);
         
-        bool have_indent = false;
-        if (!field_is_required(*m_iter)) {
-            out << indent() << "if( this.__isset." << normalize_name((*m_iter)->get_name()) << ")" << endl;
-            indent_up();
-            have_indent = true;
-        } 
-        else if( type_can_be_null(ttype)) {
-            out << indent() << "if( this." << prop_name(*m_iter) << " != null)" << endl;
-            indent_up();
-            have_indent = true;
-        } 
+        bool is_required = field_is_required(*m_iter);
+        generate_null_check_begin( out, *m_iter);
 
         out << indent() << tmp_instance << "." << prop_name(*m_iter) << " = ";
         if( needs_typecast) {
@@ -1191,8 +1182,10 @@
         }
         out << "this." << prop_name(*m_iter) << copy_op << ";" << endl;
 
-        if (have_indent) {
-            indent_down();
+        generate_null_check_end( out, *m_iter);
+        if( !is_required) {
+            out << indent() << tmp_instance << ".__isset." << normalize_name((*m_iter)->get_name())
+                 << " = this.__isset." << normalize_name((*m_iter)->get_name()) << ";" << endl;
         }
     }
 
@@ -1306,6 +1299,44 @@
     out << indent() << "}" << endl << endl;
 }
 
+
+void t_netstd_generator::generate_null_check_begin(ostream& out, t_field* tfield) {
+    bool is_required = field_is_required(tfield);
+    bool null_allowed = type_can_be_null(tfield->get_type());
+    
+    if( null_allowed || (!is_required)) {
+        bool first = true;
+        out << indent() << "if(";
+        
+        if( null_allowed) {
+            out << "(" << prop_name(tfield) << " != null)";
+            first = false;
+        }
+    
+        if( !is_required) {
+            if( !first) {
+                out << " && ";
+            }
+            out << "__isset." << normalize_name(tfield->get_name());
+        }
+        
+        out << ")" << endl
+            << indent() << "{" << endl;
+        indent_up();
+    }        
+}
+
+
+void t_netstd_generator::generate_null_check_end(ostream& out, t_field* tfield) {
+    bool is_required = field_is_required(tfield);
+    bool null_allowed = type_can_be_null(tfield->get_type());
+    
+    if( null_allowed || (!is_required)) {
+        indent_down();
+        out << indent() << "}" << endl;
+    }
+}
+
 void t_netstd_generator::generate_netstd_struct_writer(ostream& out, t_struct* tstruct)
 {
     out << indent() << "public async Task WriteAsync(TProtocol oprot, CancellationToken cancellationToken)" << endl
@@ -1329,23 +1360,7 @@
         out << indent() << "var field = new TField();" << endl;
         for (f_iter = fields.begin(); f_iter != fields.end(); ++f_iter)
         {
-            bool is_required = field_is_required(*f_iter);
-            if (!is_required)
-            {
-                bool null_allowed = type_can_be_null((*f_iter)->get_type());
-                if (null_allowed)
-                {
-                    out << indent() << "if (" << prop_name(*f_iter) << " != null && __isset." << normalize_name((*f_iter)->get_name()) << ")" << endl
-                        << indent() << "{" << endl;
-                    indent_up();
-                }
-                else
-                {
-                    out << indent() << "if (__isset." << normalize_name((*f_iter)->get_name()) << ")" << endl
-                        << indent() << "{" << endl;
-                    indent_up();
-                }
-            }
+            generate_null_check_begin( out, *f_iter);
             out << indent() << "field.Name = \"" << (*f_iter)->get_name() << "\";" << endl
                 << indent() << "field.Type = " << type_to_enum((*f_iter)->get_type()) << ";" << endl
                 << indent() << "field.ID = " << (*f_iter)->get_key() << ";" << endl
@@ -1354,11 +1369,7 @@
             generate_serialize_field(out, *f_iter);
 
             out << indent() << "await oprot.WriteFieldEndAsync(cancellationToken);" << endl;
-            if (!is_required)
-            {
-                indent_down();
-                out << indent() << "}" << endl;
-            }
+            generate_null_check_end(out, *f_iter);
         }
     }
 
@@ -1482,23 +1493,8 @@
 
     for (f_iter = fields.begin(); f_iter != fields.end(); ++f_iter)
     {
-        bool is_required = field_is_required((*f_iter));
-        if (!is_required)
-        {
-            bool null_allowed = type_can_be_null((*f_iter)->get_type());
-            if (null_allowed)
-            {
-                out << indent() << "if (" << prop_name((*f_iter)) << " != null && __isset." << normalize_name((*f_iter)->get_name()) << ")" << endl
-                    << indent() << "{" << endl;
-                indent_up();
-            }
-            else
-            {
-                out << indent() << "if (__isset." << normalize_name((*f_iter)->get_name()) << ")" << endl
-                    << indent() << "{" << endl;
-                indent_up();
-            }
-        }
+        bool is_required = field_is_required(*f_iter);
+        generate_null_check_begin(out, *f_iter);
 
         if (useFirstFlag && (!had_required))
         {
@@ -1512,13 +1508,8 @@
 
         out << indent() << prop_name(*f_iter) << ".ToString(sb);" << endl;
 
-        if (!is_required)
-        {
-            indent_down();
-            out << indent() << "}" << endl;
-        }
-        else
-        {
+        generate_null_check_end(out, *f_iter);
+        if (is_required) {
             had_required = true; // now __count must be > 0, so we don't need to check it anymore
         }
     }
@@ -1859,26 +1850,18 @@
     for (f_iter = fields.begin(); f_iter != fields.end(); ++f_iter)
     {
         t_type* ttype = (*f_iter)->get_type();
-        if (!field_is_required((*f_iter)))
-        {
-            out << indent() << "if(__isset." << normalize_name((*f_iter)->get_name()) << ")" << endl;
-            indent_up();
-        }
+
+        generate_null_check_begin(out, *f_iter);
         out << indent() << "hashcode = (hashcode * 397) + ";
-        if (ttype->is_container())
-        {
+        if (ttype->is_container()) {
             out << "TCollections.GetHashCode(" << prop_name((*f_iter)) << ")";
         }
-        else
-        {
+        else {
             out << prop_name((*f_iter)) << ".GetHashCode()";
         }
         out << ";" << endl;
 
-        if (!field_is_required((*f_iter)))
-        {
-            indent_down();
-        }
+        generate_null_check_end(out, *f_iter);
     }
 
     indent_down();
diff --git a/compiler/cpp/src/thrift/generate/t_netstd_generator.h b/compiler/cpp/src/thrift/generate/t_netstd_generator.h
index ccbd902..94ad161 100644
--- a/compiler/cpp/src/thrift/generate/t_netstd_generator.h
+++ b/compiler/cpp/src/thrift/generate/t_netstd_generator.h
@@ -171,4 +171,6 @@
   void collect_extensions_types(t_type* ttype);
   void generate_extensions(ostream& out, map<string, t_type*> types);
   void reset_indent();
+  void generate_null_check_begin(ostream& out, t_field* tfield);
+  void generate_null_check_end(ostream& out, t_field* tfield);
 };
diff --git a/lib/netstd/Tests/Thrift.Tests/DataModel/NullValuesSet.cs b/lib/netstd/Tests/Thrift.Tests/DataModel/NullValuesSet.cs
new file mode 100644
index 0000000..693b68e
--- /dev/null
+++ b/lib/netstd/Tests/Thrift.Tests/DataModel/NullValuesSet.cs
@@ -0,0 +1,101 @@
+// Licensed to the Apache Software Foundation(ASF) under one
+// or more contributor license agreements.See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+// 
+//     http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Text;
+using Microsoft.VisualStudio.TestPlatform.ObjectModel;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using OptReqDefTest;
+using Thrift.Collections;
+
+namespace Thrift.Tests.DataModel
+{
+    // ReSharper disable once InconsistentNaming
+    [TestClass]
+    public class Thrift_5238
+    {
+        private void CheckInstance(RaceDetails instance)
+        {
+            // object
+            Assert.IsTrue(instance.__isset.def_nested);
+            Assert.IsTrue(instance.__isset.opt_nested);
+            Assert.IsNull(instance.Def_nested);
+            Assert.IsNull(instance.Opt_nested);
+
+            // string
+            Assert.IsTrue(instance.__isset.def_four);
+            Assert.IsTrue(instance.__isset.opt_four);
+            Assert.IsNull(instance.Req_four);
+            Assert.IsNull(instance.Def_four);
+            Assert.IsNull(instance.Opt_four);
+
+            // byte[]
+            Assert.IsTrue(instance.__isset.def_five);
+            Assert.IsTrue(instance.__isset.opt_five);
+            Assert.IsNull(instance.Req_five);
+            Assert.IsNull(instance.Def_five);
+            Assert.IsNull(instance.Opt_five);
+
+            // list<>
+            Assert.IsTrue(instance.__isset.def_six);
+            Assert.IsTrue(instance.__isset.opt_six);
+            Assert.IsNull(instance.Req_six);
+            Assert.IsNull(instance.Opt_six);
+            Assert.IsNull(instance.Def_six);
+        }
+
+        [TestMethod]
+        public void Thrift_5238_ProperNullChecks()
+        {
+            var instance = new OptReqDefTest.RaceDetails();
+
+            // object
+            instance.Def_nested = null;
+            instance.Opt_nested = null;
+
+            // string
+            instance.Req_four = null;
+            instance.Def_four = null;
+            instance.Opt_four = null;
+
+            // byte[]
+            instance.Req_five = null;
+            instance.Def_five = null;
+            instance.Opt_five = null;
+
+            // list<>
+            instance.Req_six = null;
+            instance.Opt_six = null;
+            instance.Def_six = null;
+
+            // test the setup
+            CheckInstance(instance);
+
+            // validate proper null checks , any of these throws if not
+            instance.ToString();
+            instance.GetHashCode();
+
+            // validate proper null checks , any of these throws if not
+            var copy = instance.DeepCopy();
+            CheckInstance(copy);
+        }
+
+    }
+}