diff --git a/src/DotNetCore.CAP.AmazonSQS/AmazonPolicyExtensions.cs b/src/DotNetCore.CAP.AmazonSQS/AmazonPolicyExtensions.cs
index d3af025..1f9c652 100644
--- a/src/DotNetCore.CAP.AmazonSQS/AmazonPolicyExtensions.cs
+++ b/src/DotNetCore.CAP.AmazonSQS/AmazonPolicyExtensions.cs
@@ -209,7 +209,7 @@ namespace DotNetCore.CAP.AmazonSQS
         /// </summary>
         /// <param name="arn">Source ARN</param>
         /// <returns>Group prefix or null if group not present</returns>
-        private static string GetArnGroupPrefix(string arn)
+        private static string? GetArnGroupPrefix(string arn)
         {
             const char separator = '-';
             if (string.IsNullOrEmpty(arn) || !arn.Contains(separator))
@@ -235,7 +235,7 @@ namespace DotNetCore.CAP.AmazonSQS
         /// </summary>
         /// <param name="arn">Source ARN</param>
         /// <returns>Group name or null if group not present</returns>
-        private static string GetGroupName(string arn)
+        private static string? GetGroupName(string arn)
         {
             const char separator = ':';
             if (string.IsNullOrEmpty(arn) || !arn.Contains(separator))
diff --git a/src/DotNetCore.CAP.AmazonSQS/AmazonSQSConsumerClient.cs b/src/DotNetCore.CAP.AmazonSQS/AmazonSQSConsumerClient.cs
index 9c1a463..01dca36 100644
--- a/src/DotNetCore.CAP.AmazonSQS/AmazonSQSConsumerClient.cs
+++ b/src/DotNetCore.CAP.AmazonSQS/AmazonSQSConsumerClient.cs
@@ -27,8 +27,8 @@ namespace DotNetCore.CAP.AmazonSQS
         private readonly string _groupId;
         private readonly AmazonSQSOptions _amazonSQSOptions;
 
-        private IAmazonSimpleNotificationService _snsClient;
-        private IAmazonSQS _sqsClient;
+        private IAmazonSimpleNotificationService? _snsClient;
+        private IAmazonSQS? _sqsClient;
         private string _queueUrl = string.Empty;
 
         public AmazonSQSConsumerClient(string groupId, IOptions<AmazonSQSOptions> options)
@@ -37,9 +37,9 @@ namespace DotNetCore.CAP.AmazonSQS
             _amazonSQSOptions = options.Value;
         }
 
-        public event EventHandler<TransportMessage> OnMessageReceived;
+        public event EventHandler<TransportMessage>? OnMessageReceived;
 
-        public event EventHandler<LogMessageEventArgs> OnLog;
+        public event EventHandler<LogMessageEventArgs>? OnLog;
 
         public BrokerAddress BrokerAddress => new BrokerAddress("AmazonSQS", _queueUrl);
 
@@ -57,7 +57,7 @@ namespace DotNetCore.CAP.AmazonSQS
             {
                 var createTopicRequest = new CreateTopicRequest(topic.NormalizeForAws());
 
-                var createTopicResponse = _snsClient.CreateTopicAsync(createTopicRequest).GetAwaiter().GetResult();
+                var createTopicResponse = _snsClient!.CreateTopicAsync(createTopicRequest).GetAwaiter().GetResult();
 
                 topicArns.Add(createTopicResponse.TopicArn);
             }
@@ -92,13 +92,13 @@ namespace DotNetCore.CAP.AmazonSQS
 
             while (true)
             {
-                var response = _sqsClient.ReceiveMessageAsync(request, cancellationToken).GetAwaiter().GetResult();
+                var response = _sqsClient!.ReceiveMessageAsync(request, cancellationToken).GetAwaiter().GetResult();
 
                 if (response.Messages.Count == 1)
                 {
                     var messageObj = JsonSerializer.Deserialize<SQSReceivedMessage>(response.Messages[0].Body);
 
-                    var header = messageObj.MessageAttributes.ToDictionary(x => x.Key, x => x.Value.Value);
+                    var header = messageObj!.MessageAttributes.ToDictionary(x => x.Key, x => x.Value.Value);
                     var body = messageObj.Message;
 
                     var message = new TransportMessage(header, body != null ? Encoding.UTF8.GetBytes(body) : null);
@@ -119,7 +119,7 @@ namespace DotNetCore.CAP.AmazonSQS
         {
             try
             {
-                _ = _sqsClient.DeleteMessageAsync(_queueUrl, (string)sender).GetAwaiter().GetResult();
+                _ = _sqsClient!.DeleteMessageAsync(_queueUrl, (string)sender).GetAwaiter().GetResult();
             }
             catch (InvalidIdFormatException ex)
             {
@@ -127,12 +127,12 @@ namespace DotNetCore.CAP.AmazonSQS
             }
         }
 
-        public void Reject(object sender)
+        public void Reject(object? sender)
         {
             try
             {
                 // Visible again in 3 seconds
-                _ = _sqsClient.ChangeMessageVisibilityAsync(_queueUrl, (string)sender, 3).GetAwaiter().GetResult();
+                _ = _sqsClient!.ChangeMessageVisibilityAsync(_queueUrl, (string)sender!, 3).GetAwaiter().GetResult();
             }
             catch (MessageNotInflightException ex)
             {
@@ -237,7 +237,7 @@ namespace DotNetCore.CAP.AmazonSQS
         {
             Connect(initSNS: false, initSQS: true);
 
-            var queueAttributes = await _sqsClient.GetAttributesAsync(_queueUrl).ConfigureAwait(false);
+            var queueAttributes = await _sqsClient!.GetAttributesAsync(_queueUrl).ConfigureAwait(false);
 
             var sqsQueueArn = queueAttributes["QueueArn"];
 
@@ -263,12 +263,12 @@ namespace DotNetCore.CAP.AmazonSQS
         
         private async Task SubscribeToTopics(IEnumerable<string> topics)
         {
-            var queueAttributes = await _sqsClient.GetAttributesAsync(_queueUrl).ConfigureAwait(false);
+            var queueAttributes = await _sqsClient!.GetAttributesAsync(_queueUrl).ConfigureAwait(false);
 
             var sqsQueueArn = queueAttributes["QueueArn"];
             foreach (var topicArn in topics)
             {
-                await _snsClient.SubscribeAsync(new SubscribeRequest
+                await _snsClient!.SubscribeAsync(new SubscribeRequest
                     {
                         TopicArn = topicArn,
                         Protocol = "sqs",
diff --git a/src/DotNetCore.CAP.AmazonSQS/CAP.AmazonSQSOptions.cs b/src/DotNetCore.CAP.AmazonSQS/CAP.AmazonSQSOptions.cs
index f8dcfd5..4fdf3f2 100644
--- a/src/DotNetCore.CAP.AmazonSQS/CAP.AmazonSQSOptions.cs
+++ b/src/DotNetCore.CAP.AmazonSQS/CAP.AmazonSQSOptions.cs
@@ -10,19 +10,19 @@ namespace DotNetCore.CAP
     // ReSharper disable once InconsistentNaming
     public class AmazonSQSOptions
     {
-        public RegionEndpoint Region { get; set; }
+        public RegionEndpoint Region { get; set; } = default!;
 
-        public AWSCredentials Credentials { get; set; }
+        public AWSCredentials? Credentials { get; set; }
 
         /// <summary>
         /// Overrides Service Url deduced from AWS Region. To use in local development environments like localstack.
         /// </summary>
-        public string SNSServiceUrl { get; set; }
+        public string? SNSServiceUrl { get; set; }
 
         /// <summary>
         /// Overrides Service Url deduced from AWS Region. To use in local development environments like localstack.
         /// </summary>
-        public string SQSServiceUrl { get; set; }
+        public string? SQSServiceUrl { get; set; }
 
     }
 }
\ No newline at end of file
diff --git a/src/DotNetCore.CAP.AmazonSQS/DotNetCore.CAP.AmazonSQS.csproj b/src/DotNetCore.CAP.AmazonSQS/DotNetCore.CAP.AmazonSQS.csproj
index 6518763..9cd09e5 100644
--- a/src/DotNetCore.CAP.AmazonSQS/DotNetCore.CAP.AmazonSQS.csproj
+++ b/src/DotNetCore.CAP.AmazonSQS/DotNetCore.CAP.AmazonSQS.csproj
@@ -2,12 +2,12 @@
   
   <PropertyGroup>
     <TargetFramework>netstandard2.1</TargetFramework>
-    <AssemblyName>DotNetCore.CAP.AmazonSQS</AssemblyName>
+	<Nullable>enable</Nullable>
     <PackageTags>$(PackageTags);AmazonSQS;SQS</PackageTags>
   </PropertyGroup>
   
   <PropertyGroup>
-    <DocumentationFile>bin\$(Configuration)\netstandard2.1\DotNetCore.CAP.AmazonSQS.xml</DocumentationFile>
+	<GenerateDocumentationFile>true</GenerateDocumentationFile>
     <NoWarn>1701;1702;1705;CS1591</NoWarn>
   </PropertyGroup>
 
diff --git a/src/DotNetCore.CAP.AmazonSQS/ITransport.AmazonSQS.cs b/src/DotNetCore.CAP.AmazonSQS/ITransport.AmazonSQS.cs
index 44c8583..0bbb8b9 100644
--- a/src/DotNetCore.CAP.AmazonSQS/ITransport.AmazonSQS.cs
+++ b/src/DotNetCore.CAP.AmazonSQS/ITransport.AmazonSQS.cs
@@ -22,8 +22,8 @@ namespace DotNetCore.CAP.AmazonSQS
         private readonly ILogger _logger;
         private readonly IOptions<AmazonSQSOptions> _sqsOptions;
         private readonly SemaphoreSlim _semaphore = new SemaphoreSlim(1, 1);
-        private IAmazonSimpleNotificationService _snsClient;
-        private IDictionary<string, string> _topicArnMaps;
+        private IAmazonSimpleNotificationService? _snsClient;
+        private IDictionary<string, string>? _topicArnMaps;
 
         public AmazonSQSTransport(ILogger<AmazonSQSTransport> logger, IOptions<AmazonSQSOptions> sqsOptions)
         {
@@ -41,7 +41,7 @@ namespace DotNetCore.CAP.AmazonSQS
 
                 if (TryGetOrCreateTopicArn(message.GetName().NormalizeForAws(), out var arn))
                 {
-                    string bodyJson = null;
+                    string? bodyJson = null;
                     if (message.Body != null)
                     {
                         bodyJson = Encoding.UTF8.GetString(message.Body);
@@ -59,7 +59,7 @@ namespace DotNetCore.CAP.AmazonSQS
                         MessageAttributes = attributes
                     };
 
-                    await _snsClient.PublishAsync(request);
+                    await _snsClient!.PublishAsync(request);
 
                     _logger.LogDebug($"SNS topic message [{message.GetName().NormalizeForAws()}] has been published.");
                     return OperateResult.Success;
@@ -117,7 +117,7 @@ namespace DotNetCore.CAP.AmazonSQS
                 {
                     _topicArnMaps = new Dictionary<string, string>();
                     
-                    string nextToken = null;
+                    string? nextToken = null;
                     do
                     {
                         var topics = nextToken == null
@@ -143,15 +143,15 @@ namespace DotNetCore.CAP.AmazonSQS
             }
         }
         
-        private bool TryGetOrCreateTopicArn(string topicName, out string topicArn)
+        private bool TryGetOrCreateTopicArn(string topicName,[System.Diagnostics.CodeAnalysis.NotNullWhen(true)] out string? topicArn)
         {
             topicArn = null;
-            if (_topicArnMaps.TryGetValue(topicName, out topicArn))
+            if (_topicArnMaps!.TryGetValue(topicName, out topicArn))
             {
                 return true;
             }
 
-            var response = _snsClient.CreateTopicAsync(topicName).GetAwaiter().GetResult();
+            var response = _snsClient!.CreateTopicAsync(topicName).GetAwaiter().GetResult();
 
             if (string.IsNullOrEmpty(response.TopicArn))
             {
diff --git a/src/DotNetCore.CAP.AmazonSQS/SQSReceivedMessage.cs b/src/DotNetCore.CAP.AmazonSQS/SQSReceivedMessage.cs
index 893b418..53fcd64 100644
--- a/src/DotNetCore.CAP.AmazonSQS/SQSReceivedMessage.cs
+++ b/src/DotNetCore.CAP.AmazonSQS/SQSReceivedMessage.cs
@@ -4,15 +4,15 @@ namespace DotNetCore.CAP.AmazonSQS
 {
     class SQSReceivedMessage
     {
-        public string Message { get; set; }
+        public string? Message { get; set; }
 
-        public Dictionary<string, SQSReceivedMessageAttributes> MessageAttributes { get; set; }
+        public Dictionary<string, SQSReceivedMessageAttributes> MessageAttributes { get; set; } = default!;
     }
 
     class SQSReceivedMessageAttributes
     {
-        public string Type { get; set; }
+        public string? Type { get; set; }
 
-        public string Value { get; set; }
+        public string? Value { get; set; }
     }
 }