diff --git a/build/dependencies.props b/build/dependencies.props
index 2134695c4..451dfddd2 100644
--- a/build/dependencies.props
+++ b/build/dependencies.props
@@ -13,7 +13,7 @@
     <MicrosoftAspNetCoreSignalRPackageVersion>1.0.0</MicrosoftAspNetCoreSignalRPackageVersion>
     <MicrosoftAspNetCoreLocalizationPackageVersion>2.1.0</MicrosoftAspNetCoreLocalizationPackageVersion>
     <SystemBuffersPackageVersion>4.5.1</SystemBuffersPackageVersion>
-    <SystemMemoryPackageVersion>4.5.4</SystemMemoryPackageVersion>
+    <SystemMemoryPackageVersion>4.5.5</SystemMemoryPackageVersion>
     <SystemRuntimeCompilerServicesUnsafePackageVersion>6.0.0</SystemRuntimeCompilerServicesUnsafePackageVersion>
     <AzureIdentityPackageVersion>1.11.4</AzureIdentityPackageVersion>
     <MicrosoftExtensionsLoggingPackageVersion>2.1.0</MicrosoftExtensionsLoggingPackageVersion>
diff --git a/src/Microsoft.Azure.SignalR.Management/WebsocketsHubLifetimeManager.cs b/src/Microsoft.Azure.SignalR.Management/WebsocketsHubLifetimeManager.cs
index ec20550e1..ee5983391 100644
--- a/src/Microsoft.Azure.SignalR.Management/WebsocketsHubLifetimeManager.cs
+++ b/src/Microsoft.Azure.SignalR.Management/WebsocketsHubLifetimeManager.cs
@@ -1,6 +1,6 @@
 // Copyright (c) Microsoft. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
-
+#nullable enable
 using System;
 using System.Threading;
 using System.Threading.Tasks;
diff --git a/src/Microsoft.Azure.SignalR.Protocols/ConnectionMessage.cs b/src/Microsoft.Azure.SignalR.Protocols/ConnectionMessage.cs
index 297170049..1e2dd9bff 100644
--- a/src/Microsoft.Azure.SignalR.Protocols/ConnectionMessage.cs
+++ b/src/Microsoft.Azure.SignalR.Protocols/ConnectionMessage.cs
@@ -54,7 +54,7 @@ public OpenConnectionMessage(string connectionId, Claim[]? claims)
         /// <param name="claims">An array of <see cref="Claim"/> associated with the connection.</param>
         /// <param name="headers">A <see cref="IDictionary{TKey,TValue}"/> associated with the connection.</param>
         /// <param name="queryString">Query string associated with the connection.</param>
-        public OpenConnectionMessage(string connectionId, Claim[]? claims, IDictionary<string, StringValues> headers, string queryString)
+        public OpenConnectionMessage(string connectionId, Claim[]? claims, IDictionary<string, StringValues> headers, string? queryString)
             : base(connectionId)
         {
             Claims = claims ?? [];
@@ -75,7 +75,7 @@ public OpenConnectionMessage(string connectionId, Claim[]? claims, IDictionary<s
         /// <summary>
         /// Gets or sets the associated query string.
         /// </summary>
-        public string QueryString { get; set; }
+        public string? QueryString { get; set; }
 
         /// <summary>
         /// Gets or sets the protocol for new connection.
@@ -99,7 +99,7 @@ public class CloseConnectionMessage : ConnectionMessage, IMessageWithTracingId
         /// <param name="connectionId">The connection Id.</param>
         /// <param name="errorMessage">Optional error message.</param>
         /// <param name="headers">A <see cref="IDictionary{TKey,TValue}"/> associated with the connection.</param>
-        public CloseConnectionMessage(string connectionId, string errorMessage, IDictionary<string, StringValues>? headers = null) : base(connectionId)
+        public CloseConnectionMessage(string connectionId, string? errorMessage, IDictionary<string, StringValues>? headers = null) : base(connectionId)
         {
             ErrorMessage = errorMessage ?? "";
             Headers = headers ?? new Dictionary<string, StringValues>();
@@ -230,7 +230,7 @@ public class ClientCompletionMessage : ServiceCompletionMessage, IHasProtocol
         /// <param name="protocol">The protocol of the connection.</param>
         /// <param name="payload">The payload of the completion result.</param>
         /// <param name="tracingId">The tracing Id of the message.</param>
-        public ClientCompletionMessage(string invocationId, string connectionId, string callerServerId, string protocol, ReadOnlyMemory<byte> payload, ulong? tracingId = null)
+        public ClientCompletionMessage(string invocationId, string connectionId, string callerServerId, string? protocol, ReadOnlyMemory<byte> payload, ulong? tracingId = null)
             : base(invocationId, connectionId, callerServerId, tracingId)
         {
             Protocol = protocol;
@@ -261,10 +261,10 @@ public class ErrorCompletionMessage : ServiceCompletionMessage
         /// <param name="callerServerId">The serverId that wrap the completion result.</param>
         /// <param name="error">The error information about invacation failure.</param>
         /// <param name="tracingId">The tracing Id of the message.</param>
-        public ErrorCompletionMessage(string invocationId, string connectionId, string callerServerId, string error, ulong? tracingId = null)
+        public ErrorCompletionMessage(string invocationId, string connectionId, string callerServerId, string? error, ulong? tracingId = null)
             : base(invocationId, connectionId, callerServerId, tracingId)
         {
-            Error = error;
+            Error = error ?? string.Empty;
         }
 
         /// <summary>
diff --git a/src/Microsoft.Azure.SignalR.Protocols/GroupMessage.cs b/src/Microsoft.Azure.SignalR.Protocols/GroupMessage.cs
index 8a39a3807..da3266cc6 100644
--- a/src/Microsoft.Azure.SignalR.Protocols/GroupMessage.cs
+++ b/src/Microsoft.Azure.SignalR.Protocols/GroupMessage.cs
@@ -53,7 +53,7 @@ public class LeaveGroupMessage : ExtensibleServiceMessage, IMessageWithTracingId
         /// <summary>
         /// Gets or sets the group name.
         /// </summary>
-        public string GroupName { get; set; }
+        public string? GroupName { get; set; }
 
         /// <summary>
         /// Gets or sets the tracing Id
@@ -68,7 +68,7 @@ public class LeaveGroupMessage : ExtensibleServiceMessage, IMessageWithTracingId
         /// <param name="connectionId">The connection Id.</param>
         /// <param name="groupName">The group name, from which the connection will leave.</param>
         /// <param name="tracingId">The tracing Id of the message.</param>
-        public LeaveGroupMessage(string connectionId, string groupName, ulong? tracingId = null)
+        public LeaveGroupMessage(string connectionId, string? groupName, ulong? tracingId = null)
         {
             ConnectionId = connectionId;
             GroupName = groupName;
@@ -130,7 +130,7 @@ public class UserLeaveGroupMessage : ExtensibleServiceMessage, IMessageWithTraci
         /// <summary>
         /// Gets or sets the group name.
         /// </summary>
-        public string GroupName { get; set; }
+        public string? GroupName { get; set; }
         
         /// <summary>
         /// Gets or sets the tracing Id
@@ -145,7 +145,7 @@ public class UserLeaveGroupMessage : ExtensibleServiceMessage, IMessageWithTraci
         /// <param name="userId">The user Id.</param>
         /// <param name="groupName">The group name, from which the user will leave.</param>
         /// <param name="tracingId">The tracing Id of the message.</param>
-        public UserLeaveGroupMessage(string userId, string groupName, ulong? tracingId = null)
+        public UserLeaveGroupMessage(string userId, string? groupName, ulong? tracingId = null)
         {
             UserId = userId;
             GroupName = groupName;
@@ -216,7 +216,7 @@ public class UserLeaveGroupWithAckMessage : ExtensibleServiceMessage, IMessageWi
         /// <summary>
         /// Gets or sets the group name.
         /// </summary>
-        public string GroupName { get; set; }
+        public string? GroupName { get; set; }
 
         /// <summary>
         /// Gets or sets the tracing Id
@@ -237,7 +237,7 @@ public class UserLeaveGroupWithAckMessage : ExtensibleServiceMessage, IMessageWi
         /// <param name="groupName">The group name, from which the user will leave.</param>
         /// <param name="ackId">The ack Id.</param>
         /// <param name="tracingId">The tracing Id of the message.</param>
-        public UserLeaveGroupWithAckMessage(string userId, string groupName, int ackId, ulong? tracingId = null)
+        public UserLeaveGroupWithAckMessage(string userId, string? groupName, int ackId, ulong? tracingId = null)
         {
             UserId = userId;
             GroupName = groupName;
@@ -312,7 +312,7 @@ public class LeaveGroupWithAckMessage : ExtensibleServiceMessage, IAckableMessag
         /// <summary>
         /// Gets or sets the group name.
         /// </summary>
-        public string GroupName { get; set; }
+        public string? GroupName { get; set; }
 
         /// <summary>
         /// Gets or sets the ack id.
@@ -332,7 +332,7 @@ public class LeaveGroupWithAckMessage : ExtensibleServiceMessage, IAckableMessag
         /// <param name="connectionId">The connection Id.</param>
         /// <param name="groupName">The group name, from which the connection will leave.</param>
         /// <param name="tracingId">The tracing Id of the message.</param>
-        public LeaveGroupWithAckMessage(string connectionId, string groupName, ulong? tracingId = null): this(connectionId, groupName, 0, tracingId)
+        public LeaveGroupWithAckMessage(string connectionId, string? groupName, ulong? tracingId = null): this(connectionId, groupName, 0, tracingId)
         {
         }
 
@@ -343,7 +343,7 @@ public LeaveGroupWithAckMessage(string connectionId, string groupName, ulong? tr
         /// <param name="groupName">The group name, from which the connection will leave.</param>
         /// <param name="ackId">The ack Id</param>
         /// <param name="tracingId">The tracing Id of the message.</param>
-        public LeaveGroupWithAckMessage(string connectionId, string groupName, int ackId, ulong? tracingId = null)
+        public LeaveGroupWithAckMessage(string connectionId, string? groupName, int ackId, ulong? tracingId = null)
         {
             ConnectionId = connectionId;
             GroupName = groupName;
diff --git a/src/Microsoft.Azure.SignalR.Protocols/MessagePackPitfalls.cs b/src/Microsoft.Azure.SignalR.Protocols/MessagePackPitfalls.cs
new file mode 100644
index 000000000..a3fb600dd
--- /dev/null
+++ b/src/Microsoft.Azure.SignalR.Protocols/MessagePackPitfalls.cs
@@ -0,0 +1,13 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace System.Diagnostics.CodeAnalysis;
+
+[AttributeUsage(AttributeTargets.Method, Inherited = false)]
+internal sealed class DoesNotReturnAttribute : Attribute
+{
+}
diff --git a/src/Microsoft.Azure.SignalR.Protocols/Microsoft.Azure.SignalR.Protocols.csproj b/src/Microsoft.Azure.SignalR.Protocols/Microsoft.Azure.SignalR.Protocols.csproj
index f1bec5ab8..1e2b96677 100644
--- a/src/Microsoft.Azure.SignalR.Protocols/Microsoft.Azure.SignalR.Protocols.csproj
+++ b/src/Microsoft.Azure.SignalR.Protocols/Microsoft.Azure.SignalR.Protocols.csproj
@@ -4,6 +4,7 @@
     <TargetFramework>netstandard2.0</TargetFramework>
     <RootNamespace>Microsoft.Azure.SignalR.Protocol</RootNamespace>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/Microsoft.Azure.SignalR.Protocols/ServiceMessage.cs b/src/Microsoft.Azure.SignalR.Protocols/ServiceMessage.cs
index a4cd8d0f5..02da7ac0d 100644
--- a/src/Microsoft.Azure.SignalR.Protocols/ServiceMessage.cs
+++ b/src/Microsoft.Azure.SignalR.Protocols/ServiceMessage.cs
@@ -71,7 +71,7 @@ public abstract class ServiceMessage
         /// </summary>
         public virtual ServiceMessage Clone() => (MemberwiseClone() as ServiceMessage)!;
 
-        public static byte GeneratePartitionKey(string input)
+        public static byte GeneratePartitionKey(string? input)
         {
             return (byte)((input?.GetHashCode() ?? 0) & 0xFF);
         }
@@ -393,7 +393,7 @@ public class HandshakeResponseMessage : ExtensibleServiceMessage
         /// <summary>
         /// Gets or sets the optional error message.
         /// </summary>
-        public string ErrorMessage { get; set; }
+        public string? ErrorMessage { get; set; }
 
         /// <summary>
         /// Gets or sets the id of this connection.
@@ -411,7 +411,7 @@ public HandshakeResponseMessage() : this(string.Empty)
         /// Initializes a new instance of the <see cref="HandshakeResponseMessage"/> class.
         /// </summary>
         /// <param name="errorMessage">An optional response error message. A <c>null</c> or empty error message indicates a successful handshake.</param>
-        public HandshakeResponseMessage(string errorMessage)
+        public HandshakeResponseMessage(string? errorMessage)
         {
             ErrorMessage = errorMessage;
         }
@@ -427,7 +427,7 @@ public class PingMessage : ServiceMessage
         /// </summary>
         public static PingMessage Instance = new PingMessage();
 
-        public string[] Messages { get; set; } = Array.Empty<string>();
+        public string?[] Messages { get; set; } = Array.Empty<string?>();
     }
 
     /// <summary>
@@ -444,9 +444,9 @@ public class ServiceErrorMessage : ServiceMessage
         /// Initializes a new instance of the <see cref="ServiceErrorMessage"/> class.
         /// </summary>
         /// <param name="errorMessage">An error message.</param>
-        public ServiceErrorMessage(string errorMessage)
+        public ServiceErrorMessage(string? errorMessage)
         {
-            ErrorMessage = errorMessage;
+            ErrorMessage = errorMessage ?? string.Empty;
         }
     }
 
@@ -463,7 +463,7 @@ public class ServiceEventMessage : ExtensibleServiceMessage
         /// <summary>
         /// Gets or sets the id of event object.
         /// </summary>
-        public string Id { get; set; }
+        public string? Id { get; set; }
 
         /// <summary>
         /// Gets or sets the kind of event.
@@ -482,12 +482,12 @@ public class ServiceEventMessage : ExtensibleServiceMessage
         /// <param name="id">An id of event object.</param>
         /// <param name="kind">A kind of event.</param>
         /// <param name="message">A message of event.</param>
-        public ServiceEventMessage(ServiceEventObjectType type, string id, ServiceEventKind kind, string message)
+        public ServiceEventMessage(ServiceEventObjectType type, string? id, ServiceEventKind kind, string? message)
         {
             Type = type;
             Id = id;
             Kind = kind;
-            Message = message;
+            Message = message ?? string.Empty;
         }
     }
 
@@ -526,11 +526,11 @@ public AckMessage(int ackId, int status) : this(ackId, status, string.Empty)
         /// <param name="ackId">The ack Id</param>
         /// <param name="status">The status code</param>
         /// <param name="message">The ack message</param>
-        public AckMessage(int ackId, int status, string message)
+        public AckMessage(int ackId, int status, string? message)
         {
             AckId = ackId;
             Status = status;
-            Message = message;
+            Message = message ?? string.Empty;
         }
     }
 
diff --git a/src/Microsoft.Azure.SignalR.Protocols/ServiceProtocol.cs b/src/Microsoft.Azure.SignalR.Protocols/ServiceProtocol.cs
index 133a770a3..a258e536a 100644
--- a/src/Microsoft.Azure.SignalR.Protocols/ServiceProtocol.cs
+++ b/src/Microsoft.Azure.SignalR.Protocols/ServiceProtocol.cs
@@ -12,8 +12,6 @@
 
 namespace Microsoft.Azure.SignalR.Protocol;
 
-#nullable enable
-
 /// <summary>
 /// Implements the Azure SignalR Service Protocol.
 /// </summary>
@@ -700,7 +698,7 @@ private static void WriteErrorCompletionMessage(ref MessagePackWriter writer, Er
         writer.Write(message.Error);
         message.WriteExtensionMembers(ref writer);
     }
-
+    
     private static void WriteServiceMappingMessage(ref MessagePackWriter writer, ServiceMappingMessage message)
     {
         writer.WriteArrayHeader(5);
@@ -849,7 +847,7 @@ private static PingMessage CreatePingMessage(ref MessagePackReader reader, int a
         if (arrayLength > 1)
         {
             var length = arrayLength - 1;
-            var values = new string[length];
+            var values = new string?[length];
             for (int i = 0; i < length; i++)
             {
                 values[i] = ReadString(ref reader, "messages[{0}]", i);
@@ -862,7 +860,7 @@ private static PingMessage CreatePingMessage(ref MessagePackReader reader, int a
 
     private static OpenConnectionMessage CreateOpenConnectionMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
         var claims = ReadClaims(ref reader);
 
         // Backward compatible with old versions
@@ -885,7 +883,7 @@ private static OpenConnectionMessage CreateOpenConnectionMessage(ref MessagePack
 
     private static CloseConnectionMessage CreateCloseConnectionMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
         var errorMessage = ReadString(ref reader, "errorMessage");
         var headers = arrayLength >= 4 ? ReadHeaders(ref reader) : new Dictionary<string, StringValues>();
         var result = new CloseConnectionMessage(connectionId, errorMessage, headers);
@@ -899,7 +897,7 @@ private static CloseConnectionMessage CreateCloseConnectionMessage(ref MessagePa
     [Obsolete]
     private static CloseConnectionWithAckMessage CreateCloseConnectionWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
         var reason = ReadString(ref reader, "reason");
         var ackId = ReadInt32(ref reader, "ackId");
         var result = new CloseConnectionWithAckMessage(connectionId, ackId)
@@ -934,7 +932,7 @@ private static CloseConnectionsWithAckMessage CreateCloseConnectionsWithAckMessa
 
     private static CloseUserConnectionsWithAckMessage CreateCloseUserConnectionsWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var userId = ReadString(ref reader, "userId");
+        var userId = ReadStringNotNull(ref reader, "userId");
         var reason = ReadString(ref reader, "reason");
         var ackId = ReadInt32(ref reader, "ackId");
         var excluded = ReadStringArray(ref reader, "excluded");
@@ -953,7 +951,7 @@ private static CloseUserConnectionsWithAckMessage CreateCloseUserConnectionsWith
 
     private static CloseGroupConnectionsWithAckMessage CreateCloseGroupConnectionsWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var group = ReadString(ref reader, "group");
+        var group = ReadStringNotNull(ref reader, "group");
         var reason = ReadString(ref reader, "reason");
         var ackId = ReadInt32(ref reader, "ackId");
         var excluded = ReadStringArray(ref reader, "excluded");
@@ -972,7 +970,7 @@ private static CloseGroupConnectionsWithAckMessage CreateCloseGroupConnectionsWi
 
     private static ConnectionDataMessage CreateConnectionDataMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
         var payload = ReadBytes(ref reader, "payload");
 
         var result = new ConnectionDataMessage(connectionId, payload);
@@ -985,7 +983,7 @@ private static ConnectionDataMessage CreateConnectionDataMessage(ref MessagePack
 
     private static ConnectionReconnectMessage CreateConnectionReconnectMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
 
         var result = new ConnectionReconnectMessage(connectionId);
         result.ReadExtensionMembers(ref reader);
@@ -1007,7 +1005,7 @@ private static MultiConnectionDataMessage CreateMultiConnectionDataMessage(ref M
 
     private static ServiceMessage CreateUserDataMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var userId = ReadString(ref reader, "userId");
+        var userId = ReadStringNotNull(ref reader, "userId");
         var payloads = ReadPayloads(ref reader);
 
         var result = new UserDataMessage(userId, payloads);
@@ -1046,8 +1044,8 @@ private static BroadcastDataMessage CreateBroadcastDataMessage(ref MessagePackRe
 
     private static JoinGroupMessage CreateJoinGroupMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
-        var groupName = ReadString(ref reader, "groupName");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
+        var groupName = ReadStringNotNull(ref reader, "groupName");
 
         var result = new JoinGroupMessage(connectionId, groupName);
         if (arrayLength >= 4)
@@ -1059,7 +1057,7 @@ private static JoinGroupMessage CreateJoinGroupMessage(ref MessagePackReader rea
 
     private static LeaveGroupMessage CreateLeaveGroupMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
         var groupName = ReadString(ref reader, "groupName");
 
         var result = new LeaveGroupMessage(connectionId, groupName);
@@ -1072,8 +1070,8 @@ private static LeaveGroupMessage CreateLeaveGroupMessage(ref MessagePackReader r
 
     private static UserJoinGroupMessage CreateUserJoinGroupMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var userId = ReadString(ref reader, "userId");
-        var groupName = ReadString(ref reader, "groupName");
+        var userId = ReadStringNotNull(ref reader, "userId");
+        var groupName = ReadStringNotNull(ref reader, "groupName");
 
         var result = new UserJoinGroupMessage(userId, groupName);
         if (arrayLength >= 4)
@@ -1085,7 +1083,7 @@ private static UserJoinGroupMessage CreateUserJoinGroupMessage(ref MessagePackRe
 
     private static UserLeaveGroupMessage CreateUserLeaveGroupMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var userId = ReadString(ref reader, "userId");
+        var userId = ReadStringNotNull(ref reader, "userId");
         var groupName = ReadString(ref reader, "groupName");
 
         var result = new UserLeaveGroupMessage(userId, groupName);
@@ -1098,8 +1096,8 @@ private static UserLeaveGroupMessage CreateUserLeaveGroupMessage(ref MessagePack
 
     private static UserJoinGroupWithAckMessage CreateUserJoinGroupWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var userId = ReadString(ref reader, "userId");
-        var groupName = ReadString(ref reader, "groupName");
+        var userId = ReadStringNotNull(ref reader, "userId");
+        var groupName = ReadStringNotNull(ref reader, "groupName");
         var ackId = ReadInt32(ref reader, "ackId");
 
         var result = new UserJoinGroupWithAckMessage(userId, groupName, ackId);
@@ -1109,7 +1107,7 @@ private static UserJoinGroupWithAckMessage CreateUserJoinGroupWithAckMessage(ref
 
     private static UserLeaveGroupWithAckMessage CreateUserLeaveGroupWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var userId = ReadString(ref reader, "userId");
+        var userId = ReadStringNotNull(ref reader, "userId");
         var groupName = ReadString(ref reader, "groupName");
         var ackId = ReadInt32(ref reader, "ackId");
 
@@ -1120,7 +1118,7 @@ private static UserLeaveGroupWithAckMessage CreateUserLeaveGroupWithAckMessage(r
 
     private static GroupBroadcastDataMessage CreateGroupBroadcastDataMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var groupName = ReadString(ref reader, "groupName");
+        var groupName = ReadStringNotNull(ref reader, "groupName");
         var excludedList = ReadStringArray(ref reader, "excludedList");
         var payloads = ReadPayloads(ref reader);
 
@@ -1172,8 +1170,8 @@ private static ServiceEventMessage CreateServiceEventMessage(ref MessagePackRead
 
     private static JoinGroupWithAckMessage CreateJoinGroupWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
-        var groupName = ReadString(ref reader, "groupName");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
+        var groupName = ReadStringNotNull(ref reader, "groupName");
         var ackId = ReadInt32(ref reader, "ackId");
 
         var result = new JoinGroupWithAckMessage(connectionId, groupName, ackId);
@@ -1186,7 +1184,7 @@ private static JoinGroupWithAckMessage CreateJoinGroupWithAckMessage(ref Message
 
     private static LeaveGroupWithAckMessage CreateLeaveGroupWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
         var groupName = ReadString(ref reader, "groupName");
         var ackId = ReadInt32(ref reader, "ackId");
 
@@ -1200,8 +1198,8 @@ private static LeaveGroupWithAckMessage CreateLeaveGroupWithAckMessage(ref Messa
 
     private static CheckUserInGroupWithAckMessage CreateCheckUserInGroupWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var userId = ReadString(ref reader, "userId");
-        var groupName = ReadString(ref reader, "groupName");
+        var userId = ReadStringNotNull(ref reader, "userId");
+        var groupName = ReadStringNotNull(ref reader, "groupName");
         var ackId = ReadInt32(ref reader, "ackId");
 
         var result = new CheckUserInGroupWithAckMessage(userId, groupName, ackId);
@@ -1214,7 +1212,7 @@ private static CheckUserInGroupWithAckMessage CreateCheckUserInGroupWithAckMessa
 
     private static CheckGroupExistenceWithAckMessage CreateGroupExistenceWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var groupName = ReadString(ref reader, "groupName");
+        var groupName = ReadStringNotNull(ref reader, "groupName");
         var ackId = ReadInt32(ref reader, "ackId");
 
         var result = new CheckGroupExistenceWithAckMessage(groupName, ackId);
@@ -1224,7 +1222,7 @@ private static CheckGroupExistenceWithAckMessage CreateGroupExistenceWithAckMess
 
     private static CheckConnectionExistenceWithAckMessage CreateCheckConnectionExistenceWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
         var ackId = ReadInt32(ref reader, "ackId");
 
         var result = new CheckConnectionExistenceWithAckMessage(connectionId, ackId);
@@ -1234,7 +1232,7 @@ private static CheckConnectionExistenceWithAckMessage CreateCheckConnectionExist
 
     private static CheckUserExistenceWithAckMessage CreateCheckUserExistenceWithAckMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var userId = ReadString(ref reader, "userId");
+        var userId = ReadStringNotNull(ref reader, "userId");
         var ackId = ReadInt32(ref reader, "ackId");
 
         var result = new CheckUserExistenceWithAckMessage(userId, ackId);
@@ -1258,9 +1256,9 @@ private static AckMessage CreateAckMessage(ref MessagePackReader reader, int arr
 
     private static ClientInvocationMessage CreateClientInvocationMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var invocationId = ReadString(ref reader, "invocationId");
-        var connectionId = ReadString(ref reader, "connectionId");
-        var callerServerId = ReadString(ref reader, "callerServerId");
+        var invocationId = ReadStringNotNull(ref reader, "invocationId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
+        var callerServerId = ReadStringNotNull(ref reader, "callerServerId");
         var payloads = ReadPayloads(ref reader);
 
         var result = new ClientInvocationMessage(invocationId, connectionId, callerServerId, payloads);
@@ -1270,9 +1268,9 @@ private static ClientInvocationMessage CreateClientInvocationMessage(ref Message
 
     private static ClientCompletionMessage CreateClientCompletionMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var invocationId = ReadString(ref reader, "invocationId");
-        var connectionId = ReadString(ref reader, "connectionId");
-        var callerServerId = ReadString(ref reader, "callerServerId");
+        var invocationId = ReadStringNotNull(ref reader, "invocationId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
+        var callerServerId = ReadStringNotNull(ref reader, "callerServerId");
         var protocol = ReadString(ref reader, "protocol");
         var payload = ReadBytes(ref reader, "payload");
 
@@ -1284,9 +1282,9 @@ private static ClientCompletionMessage CreateClientCompletionMessage(ref Message
 
     private static ErrorCompletionMessage CreateErrorCompletionMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var invocationId = ReadString(ref reader, "invocationId");
-        var connectionId = ReadString(ref reader, "connectionId");
-        var callerServerId = ReadString(ref reader, "callerServerId");
+        var invocationId = ReadStringNotNull(ref reader, "invocationId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
+        var callerServerId = ReadStringNotNull(ref reader, "callerServerId");
         var error = ReadString(ref reader, "error");
 
         var result = new ErrorCompletionMessage(invocationId, connectionId, callerServerId, error);
@@ -1297,9 +1295,9 @@ private static ErrorCompletionMessage CreateErrorCompletionMessage(ref MessagePa
 
     private static ServiceMappingMessage CreateServiceMappingMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var invocationId = ReadString(ref reader, "invocationId");
-        var connectionId = ReadString(ref reader, "connectionId");
-        var instanceId = ReadString(ref reader, "instanceId");
+        var invocationId = ReadStringNotNull(ref reader, "invocationId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
+        var instanceId = ReadStringNotNull(ref reader, "instanceId");
 
         var result = new ServiceMappingMessage(invocationId, connectionId, instanceId);
 
@@ -1309,7 +1307,7 @@ private static ServiceMappingMessage CreateServiceMappingMessage(ref MessagePack
 
     private static ConnectionFlowControlMessage CreateConnectionFlowControlMessage(ref MessagePackReader reader, int arrayLength)
     {
-        var connectionId = ReadString(ref reader, "connectionId");
+        var connectionId = ReadStringNotNull(ref reader, "connectionId");
         var connectionType = ReadInt32(ref reader, "connectionType");
         var operation = ReadInt32(ref reader, "operation");
 
@@ -1368,7 +1366,9 @@ private static IDictionary<string, ReadOnlyMemory<byte>> ReadPayloads(ref Messag
             var payloads = new ArrayDictionary<string, ReadOnlyMemory<byte>>((int)payloadCount, StringComparer.OrdinalIgnoreCase);
             for (var i = 0; i < payloadCount; i++)
             {
-                var key = ReadString(ref reader, "payloads[{0}].key", i);
+                var keyName = $"payloads[{i}].key";
+
+                var key = ReadStringNotNull(ref reader, keyName);
                 var value = ReadBytes(ref reader, "payloads[{0}].value", i);
                 payloads.Add(key, value);
             }
@@ -1387,9 +1387,10 @@ private static IDictionary<string, StringValues> ReadHeaders(ref MessagePackRead
             var headers = new Dictionary<string, StringValues>((int)headerCount, StringComparer.OrdinalIgnoreCase);
             for (var i = 0; i < headerCount; i++)
             {
-                var key = ReadString(ref reader, $"headers[{i}].key");
+                var keyName = $"headers[{i}].key";
+                var key = ReadStringNotNull(ref reader, keyName);
                 var count = ReadArrayLength(ref reader, $"headers[{i}].value.length");
-                var stringValues = new string[count];
+                var stringValues = new string?[count];
                 for (var j = 0; j < count; j++)
                 {
                     stringValues[j] = ReadString(ref reader, $"headers[{i}].value[{j}]");
@@ -1412,6 +1413,7 @@ private static bool ReadBoolean(ref MessagePackReader reader, string field)
         catch (Exception ex)
         {
             throw new InvalidDataException($"Reading '{field}' as Boolean failed.", ex);
+
         }
     }
 
@@ -1425,10 +1427,9 @@ private static int ReadInt32(ref MessagePackReader reader, string field)
         {
             throw new InvalidDataException($"Reading '{field}' as Int32 failed.", ex);
         }
-
     }
 
-    private static string ReadString(ref MessagePackReader reader, string field)
+    private static string? ReadString(ref MessagePackReader reader, string field)
     {
         try
         {
@@ -1440,19 +1441,28 @@ private static string ReadString(ref MessagePackReader reader, string field)
         }
     }
 
-    private static string ReadString(ref MessagePackReader reader, string formatField, int param)
+    private static string ReadStringNotNull(ref MessagePackReader reader, string field)
     {
+        string? result = null;  
         try
         {
-            return reader.ReadString();
+            result = reader.ReadString();
         }
         catch (Exception ex)
         {
-            throw new InvalidDataException($"Reading '{string.Format(formatField, param)}' as String failed.", ex);
+            throw new InvalidDataException($"Reading '{field}' as String failed.", ex);
+
         }
+
+        if (result == null)
+        {
+            throw new InvalidDataException($"Reading '{field}' as Not-Null String failed.");
+        }
+
+        return result;
     }
 
-    private static string ReadString(ref MessagePackReader reader, string formatField, string param1, int param2)
+    private static string? ReadString(ref MessagePackReader reader, string formatField, int param)
     {
         try
         {
@@ -1460,7 +1470,7 @@ private static string ReadString(ref MessagePackReader reader, string formatFiel
         }
         catch (Exception ex)
         {
-            throw new InvalidDataException($"Reading '{string.Format(formatField, param1, param2)}' as String failed.", ex);
+            throw new InvalidDataException($"Reading '{string.Format(formatField, param)}' as String failed.", ex);
         }
     }
 
@@ -1472,7 +1482,8 @@ private static string[] ReadStringArray(ref MessagePackReader reader, string fie
             var array = new string[arrayLength];
             for (int i = 0; i < arrayLength; i++)
             {
-                array[i] = ReadString(ref reader, "{0}[{1}]", field, i);
+                var fieldName = $"{field}[{i}]";
+                array[i] = ReadStringNotNull(ref reader, fieldName);
             }
 
             return array;
diff --git a/src/Microsoft.Azure.SignalR.Serverless.Protocols/Internal/MessagePackReaderExtensions.cs b/src/Microsoft.Azure.SignalR.Serverless.Protocols/Internal/MessagePackReaderExtensions.cs
index d4b6c8c4f..fa3198d0b 100644
--- a/src/Microsoft.Azure.SignalR.Serverless.Protocols/Internal/MessagePackReaderExtensions.cs
+++ b/src/Microsoft.Azure.SignalR.Serverless.Protocols/Internal/MessagePackReaderExtensions.cs
@@ -24,7 +24,7 @@ public static int ReadInt32(ref this MessagePackReader reader, string field)
         }
     }
 
-    public static string ReadString(ref this MessagePackReader reader, string field)
+    public static string? ReadString(ref this MessagePackReader reader, string field)
     {
         try
         {
@@ -87,7 +87,7 @@ public static int ReadArrayLength(ref this MessagePackReader reader, string fiel
                 var map = new Dictionary<string, object?>();
                 for (var i = 0; i < propertyCount; i++)
                 {
-                    var key = reader.ReadString();
+                    var key = reader.ReadString().ThrowWhenNull();
                     var value = reader.ReadObject(field);
                     map[key] = value;
                 }
@@ -115,4 +115,8 @@ public static void SkipHeader(ref this MessagePackReader reader)
         }
     }
 
+    public static string ThrowWhenNull(this string? input)
+    {
+        return input ?? throw new ArgumentNullException(nameof(input));
+    }
 }
diff --git a/src/Microsoft.Azure.SignalR.Serverless.Protocols/MessagePackPitfalls.cs b/src/Microsoft.Azure.SignalR.Serverless.Protocols/MessagePackPitfalls.cs
new file mode 100644
index 000000000..a3fb600dd
--- /dev/null
+++ b/src/Microsoft.Azure.SignalR.Serverless.Protocols/MessagePackPitfalls.cs
@@ -0,0 +1,13 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace System.Diagnostics.CodeAnalysis;
+
+[AttributeUsage(AttributeTargets.Method, Inherited = false)]
+internal sealed class DoesNotReturnAttribute : Attribute
+{
+}
diff --git a/src/Microsoft.Azure.SignalR.Serverless.Protocols/Microsoft.Azure.SignalR.Serverless.Protocols.csproj b/src/Microsoft.Azure.SignalR.Serverless.Protocols/Microsoft.Azure.SignalR.Serverless.Protocols.csproj
index e2a9d768a..d6f53bea8 100644
--- a/src/Microsoft.Azure.SignalR.Serverless.Protocols/Microsoft.Azure.SignalR.Serverless.Protocols.csproj
+++ b/src/Microsoft.Azure.SignalR.Serverless.Protocols/Microsoft.Azure.SignalR.Serverless.Protocols.csproj
@@ -4,6 +4,7 @@
     <Description>.NET Standard SDK for Azure SignalR Service serverless protocol.</Description>
     <TargetFramework>netstandard2.0</TargetFramework>
     <RootNamespace>Microsoft.Azure.SignalR.Serverless.Protocols</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   
   <ItemGroup>
diff --git a/src/submodules/MessagePack-CSharp b/src/submodules/MessagePack-CSharp
index 38f095bf0..d3d435b96 160000
--- a/src/submodules/MessagePack-CSharp
+++ b/src/submodules/MessagePack-CSharp
@@ -1 +1 @@
-Subproject commit 38f095bf0d9b72e2f9e8484282937f433bf3dfcb
+Subproject commit d3d435b96cf09b9b0afc313bdea4257de6481c9f