diff --git a/DDTool/DDTool/Generators/GenMessageFactories.cs b/DDTool/DDTool/Generators/GenMessageFactories.cs
index 45f00206b..cc59b8e05 100644
--- a/DDTool/DDTool/Generators/GenMessageFactories.cs
+++ b/DDTool/DDTool/Generators/GenMessageFactories.cs
@@ -62,7 +62,7 @@ private static string Generate(DataDictionary dd) {
             "        };",
             "    }",
             "",
-            "    public Group Create(string beginString, string msgType, int correspondingFieldId)",
+            "    public Group? Create(string beginString, string msgType, int correspondingFieldId)",
             "    {"
         });
 
diff --git a/Messages/FIX40/MessageFactory.cs b/Messages/FIX40/MessageFactory.cs
index 33974180a..1b1f100fb 100644
--- a/Messages/FIX40/MessageFactory.cs
+++ b/Messages/FIX40/MessageFactory.cs
@@ -52,7 +52,7 @@ public QuickFix.Message Create(string beginString, string msgType)
         };
     }
 
-    public Group Create(string beginString, string msgType, int correspondingFieldId)
+    public Group? Create(string beginString, string msgType, int correspondingFieldId)
     {
         if (QuickFix.FIX40.News.MsgType.Equals(msgType))
         {
diff --git a/Messages/FIX40/QuickFix.FIX40.csproj b/Messages/FIX40/QuickFix.FIX40.csproj
index 2ff27cee1..82415947c 100644
--- a/Messages/FIX40/QuickFix.FIX40.csproj
+++ b/Messages/FIX40/QuickFix.FIX40.csproj
@@ -21,6 +21,7 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageIcon>qfn-icon.png</PackageIcon>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/Messages/FIX41/MessageFactory.cs b/Messages/FIX41/MessageFactory.cs
index fa10cf51a..3ad79eaad 100644
--- a/Messages/FIX41/MessageFactory.cs
+++ b/Messages/FIX41/MessageFactory.cs
@@ -53,7 +53,7 @@ public QuickFix.Message Create(string beginString, string msgType)
         };
     }
 
-    public Group Create(string beginString, string msgType, int correspondingFieldId)
+    public Group? Create(string beginString, string msgType, int correspondingFieldId)
     {
         if (QuickFix.FIX41.IndicationofInterest.MsgType.Equals(msgType))
         {
diff --git a/Messages/FIX41/QuickFix.FIX41.csproj b/Messages/FIX41/QuickFix.FIX41.csproj
index 54864055f..983ef5804 100644
--- a/Messages/FIX41/QuickFix.FIX41.csproj
+++ b/Messages/FIX41/QuickFix.FIX41.csproj
@@ -21,6 +21,7 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageIcon>qfn-icon.png</PackageIcon>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/Messages/FIX42/MessageFactory.cs b/Messages/FIX42/MessageFactory.cs
index 0fa23bc04..aac8c011f 100644
--- a/Messages/FIX42/MessageFactory.cs
+++ b/Messages/FIX42/MessageFactory.cs
@@ -71,7 +71,7 @@ public QuickFix.Message Create(string beginString, string msgType)
         };
     }
 
-    public Group Create(string beginString, string msgType, int correspondingFieldId)
+    public Group? Create(string beginString, string msgType, int correspondingFieldId)
     {
         if (QuickFix.FIX42.Logon.MsgType.Equals(msgType))
         {
diff --git a/Messages/FIX42/QuickFix.FIX42.csproj b/Messages/FIX42/QuickFix.FIX42.csproj
index cd225723d..8050a6527 100644
--- a/Messages/FIX42/QuickFix.FIX42.csproj
+++ b/Messages/FIX42/QuickFix.FIX42.csproj
@@ -21,6 +21,7 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageIcon>qfn-icon.png</PackageIcon>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/Messages/FIX43/MessageFactory.cs b/Messages/FIX43/MessageFactory.cs
index 6422c4852..c2b356d8d 100644
--- a/Messages/FIX43/MessageFactory.cs
+++ b/Messages/FIX43/MessageFactory.cs
@@ -93,7 +93,7 @@ public QuickFix.Message Create(string beginString, string msgType)
         };
     }
 
-    public Group Create(string beginString, string msgType, int correspondingFieldId)
+    public Group? Create(string beginString, string msgType, int correspondingFieldId)
     {
         if (QuickFix.FIX43.Logon.MsgType.Equals(msgType))
         {
diff --git a/Messages/FIX43/QuickFix.FIX43.csproj b/Messages/FIX43/QuickFix.FIX43.csproj
index 70a4707f1..a18dd8f16 100644
--- a/Messages/FIX43/QuickFix.FIX43.csproj
+++ b/Messages/FIX43/QuickFix.FIX43.csproj
@@ -21,6 +21,7 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageIcon>qfn-icon.png</PackageIcon>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/Messages/FIX44/MessageFactory.cs b/Messages/FIX44/MessageFactory.cs
index 9d957c8e4..f7bcfaf88 100644
--- a/Messages/FIX44/MessageFactory.cs
+++ b/Messages/FIX44/MessageFactory.cs
@@ -118,7 +118,7 @@ public QuickFix.Message Create(string beginString, string msgType)
         };
     }
 
-    public Group Create(string beginString, string msgType, int correspondingFieldId)
+    public Group? Create(string beginString, string msgType, int correspondingFieldId)
     {
         if (QuickFix.FIX44.Logon.MsgType.Equals(msgType))
         {
diff --git a/Messages/FIX44/QuickFix.FIX44.csproj b/Messages/FIX44/QuickFix.FIX44.csproj
index 1942848a1..f1dfb0faa 100644
--- a/Messages/FIX44/QuickFix.FIX44.csproj
+++ b/Messages/FIX44/QuickFix.FIX44.csproj
@@ -21,6 +21,7 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageIcon>qfn-icon.png</PackageIcon>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/Messages/FIX50/MessageFactory.cs b/Messages/FIX50/MessageFactory.cs
index a179a9b02..49d497ef5 100644
--- a/Messages/FIX50/MessageFactory.cs
+++ b/Messages/FIX50/MessageFactory.cs
@@ -118,7 +118,7 @@ public QuickFix.Message Create(string beginString, string msgType)
         };
     }
 
-    public Group Create(string beginString, string msgType, int correspondingFieldId)
+    public Group? Create(string beginString, string msgType, int correspondingFieldId)
     {
         if (QuickFix.FIX50.IOI.MsgType.Equals(msgType))
         {
diff --git a/Messages/FIX50/QuickFix.FIX50.csproj b/Messages/FIX50/QuickFix.FIX50.csproj
index 4e9fe2bbd..f7ac52280 100644
--- a/Messages/FIX50/QuickFix.FIX50.csproj
+++ b/Messages/FIX50/QuickFix.FIX50.csproj
@@ -21,6 +21,7 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageIcon>qfn-icon.png</PackageIcon>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/Messages/FIX50SP1/MessageFactory.cs b/Messages/FIX50SP1/MessageFactory.cs
index 63b5ed9e7..8f11ec1e5 100644
--- a/Messages/FIX50SP1/MessageFactory.cs
+++ b/Messages/FIX50SP1/MessageFactory.cs
@@ -130,7 +130,7 @@ public QuickFix.Message Create(string beginString, string msgType)
         };
     }
 
-    public Group Create(string beginString, string msgType, int correspondingFieldId)
+    public Group? Create(string beginString, string msgType, int correspondingFieldId)
     {
         if (QuickFix.FIX50SP1.IOI.MsgType.Equals(msgType))
         {
diff --git a/Messages/FIX50SP1/QuickFix.FIX50SP1.csproj b/Messages/FIX50SP1/QuickFix.FIX50SP1.csproj
index fd9c8ecd9..765a4c22e 100644
--- a/Messages/FIX50SP1/QuickFix.FIX50SP1.csproj
+++ b/Messages/FIX50SP1/QuickFix.FIX50SP1.csproj
@@ -21,6 +21,7 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageIcon>qfn-icon.png</PackageIcon>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/Messages/FIX50SP2/MessageFactory.cs b/Messages/FIX50SP2/MessageFactory.cs
index 18ed1ec04..f7350eeac 100644
--- a/Messages/FIX50SP2/MessageFactory.cs
+++ b/Messages/FIX50SP2/MessageFactory.cs
@@ -135,7 +135,7 @@ public QuickFix.Message Create(string beginString, string msgType)
         };
     }
 
-    public Group Create(string beginString, string msgType, int correspondingFieldId)
+    public Group? Create(string beginString, string msgType, int correspondingFieldId)
     {
         if (QuickFix.FIX50SP2.IOI.MsgType.Equals(msgType))
         {
diff --git a/Messages/FIX50SP2/QuickFix.FIX50SP2.csproj b/Messages/FIX50SP2/QuickFix.FIX50SP2.csproj
index dd893616c..6083a44ca 100644
--- a/Messages/FIX50SP2/QuickFix.FIX50SP2.csproj
+++ b/Messages/FIX50SP2/QuickFix.FIX50SP2.csproj
@@ -21,6 +21,7 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageIcon>qfn-icon.png</PackageIcon>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/Messages/FIXT11/MessageFactory.cs b/Messages/FIXT11/MessageFactory.cs
index 0d56585a0..66881cff9 100644
--- a/Messages/FIXT11/MessageFactory.cs
+++ b/Messages/FIXT11/MessageFactory.cs
@@ -33,7 +33,7 @@ public QuickFix.Message Create(string beginString, string msgType)
         };
     }
 
-    public Group Create(string beginString, string msgType, int correspondingFieldId)
+    public Group? Create(string beginString, string msgType, int correspondingFieldId)
     {
         if (QuickFix.FIXT11.Logon.MsgType.Equals(msgType))
         {
diff --git a/Messages/FIXT11/QuickFix.FIXT11.csproj b/Messages/FIXT11/QuickFix.FIXT11.csproj
index 61c9b7db4..f2ecc263f 100644
--- a/Messages/FIXT11/QuickFix.FIXT11.csproj
+++ b/Messages/FIXT11/QuickFix.FIXT11.csproj
@@ -21,6 +21,7 @@
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageIcon>qfn-icon.png</PackageIcon>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/QuickFIXn/DefaultMessageFactory.cs b/QuickFIXn/DefaultMessageFactory.cs
index 58dbc073b..6d0688ac6 100644
--- a/QuickFIXn/DefaultMessageFactory.cs
+++ b/QuickFIXn/DefaultMessageFactory.cs
@@ -80,7 +80,7 @@ public Message Create(string beginString, QuickFix.Fields.ApplVerID applVerId, s
             return message;
         }
 
-        public Group Create(string beginString, string msgType, int groupCounterTag)
+        public Group? Create(string beginString, string msgType, int groupCounterTag)
         {
             string key = beginString;
             if(beginString.Equals(FixValues.BeginString.FIXT11))
diff --git a/QuickFIXn/IMessageFactory.cs b/QuickFIXn/IMessageFactory.cs
index 80f91a776..949041fca 100644
--- a/QuickFIXn/IMessageFactory.cs
+++ b/QuickFIXn/IMessageFactory.cs
@@ -39,7 +39,7 @@ public interface IMessageFactory
         /// <param name="beginString">the FIX version (e.g. "FIX.4.2")</param>
         /// <param name="msgType">message type of the enclosing message (e.g. "D" for a NewOrderSingle</param>
         /// <param name="groupCounterTag">the tag of the group's counter field</param>
-        /// <returns>group, or null if the group can't be created</returns>
-        Group Create(string beginString, string msgType, int groupCounterTag);
+        /// <returns>A group, or null if the group can't be created</returns>
+        Group? Create(string beginString, string msgType, int groupCounterTag);
     }
 }
diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 5acdee982..e8273cb06 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -52,6 +52,7 @@ What's New
 * #914 - Optimize MessageCracker.IsHandlerMethod (vasily-balansea)
 * #742 - Improvements to HTTP web proxy (IanLeeClaxton)
 * #277 - change FileStore.SetSeqNum() to dispose StreamWriter (hlibman)
+* #nnn - mark IMessageFactory.Create's Group return value as nullable (gbirchmeier)
 
 ### v1.12.0
 
diff --git a/UnitTests/DefaultMessageFactoryTests.cs b/UnitTests/DefaultMessageFactoryTests.cs
index f1fdbc4f2..a69b2a15d 100644
--- a/UnitTests/DefaultMessageFactoryTests.cs
+++ b/UnitTests/DefaultMessageFactoryTests.cs
@@ -15,13 +15,13 @@ public void GroupCreateTest_Fix50()
         {
             DefaultMessageFactory dmf = new DefaultMessageFactory(QuickFix.FixValues.ApplVerID.FIX50);
 
-            Group g44 = dmf.Create("FIX.4.4", "B", 33);
+            Group? g44 = dmf.Create("FIX.4.4", "B", 33);
             Assert.That(g44, Is.InstanceOf<QuickFix.FIX44.News.LinesOfTextGroup>());
 
-            Group g50 = dmf.Create("FIXT.1.1", "B", 33);
+            Group? g50 = dmf.Create("FIXT.1.1", "B", 33);
             Assert.That(g50, Is.InstanceOf<QuickFix.FIX50.News.NoLinesOfTextGroup>());
 
-            Group g50sp2 = dmf.Create("FIXT.1.1", "CD", QuickFix.Fields.Tags.NoAsgnReqs);
+            Group? g50sp2 = dmf.Create("FIXT.1.1", "CD", QuickFix.Fields.Tags.NoAsgnReqs);
             Assert.That(g50sp2, Is.Null);
         }
 
@@ -30,10 +30,10 @@ public void GroupCreateTest_DefaultFix50Sp2()
         {
             DefaultMessageFactory dmf = new DefaultMessageFactory();
 
-            Group g44 = dmf.Create("FIX.4.4", "B", 33);
+            Group? g44 = dmf.Create("FIX.4.4", "B", 33);
             Assert.That(g44, Is.InstanceOf<QuickFix.FIX44.News.LinesOfTextGroup>());
 
-            Group g50sp2 = dmf.Create("FIXT.1.1", "CD", QuickFix.Fields.Tags.NoAsgnReqs);
+            Group? g50sp2 = dmf.Create("FIXT.1.1", "CD", QuickFix.Fields.Tags.NoAsgnReqs);
             Assert.That(g50sp2, Is.InstanceOf<QuickFix.FIX50SP2.StreamAssignmentReport.NoAsgnReqsGroup>());
         }
     }