NullReferenceException on AmazonCloudFormationClient.UpdateStackAsync for SDK v4

[greg5123334]

Describe the bug

It is a known issue when migrating from SDK v3 to v4 that Collections will return null, resulting in a NullReferenceException. The workaround is to set the static variable to pre-initialize Collectoins:

Amazon.AWSConfigs.InitializeCollections = true;

The long-term solution is to perform null-checks in code.

The problem with UpdateStackAsync however, is that the null reference is happening deep inside SDK code, not customer-facing code. The implication being, one cannot apply the fix, as it will need to be corrected in the SDK sauce itself.

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

Calling UpdateStackAsync should NOT encounter NullReferenceException.

Current Behavior

Calling UpdateStackAsync DOES encounter NullReferenceException.

Reproduction Steps

using Amazon.CloudFormation;
using Amazon.CloudFormation.Model;
using Amazon.Runtime;
using Amazon.Runtime.CredentialManagement;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;

// See https://aka.ms/new-console-template for more information
Console.WriteLine("Hello, World!");

// Workaround for System.NullReferenceException
// Amazon.AWSConfigs.InitializeCollections = true;

// Create a CloudFormation client with explicit region
var client = new AmazonCloudFormationClient(
    region: Amazon.RegionEndpoint.USEast1  // Change to your region
);

// Simple CloudFormation template for creating an SNS topic
string templateBody = @"{
  ""Resources"" : {
    ""MySNSTopic"" : {
      ""Type"" : ""AWS::SNS::Topic"",
      ""Properties"" : {
        ""DisplayName"" : ""MySampleTopic""
      }
    }
  },
  ""Outputs"" : {
    ""TopicARN"" : {
      ""Description"" : ""ARN of the SNS Topic"",
      ""Value"" : { ""Ref"" : ""MySNSTopic"" }
    }
  }
}";

// Choose which operation to perform
// await CreateStackAsync();
await UpdateStackAsync();

async Task CreateStackAsync()
{
    try
    {
        var response = await client.CreateStackAsync(new CreateStackRequest
        {
            StackName = "MySNSTopicStack",
            TemplateBody = templateBody,
            OnFailure = OnFailure.DELETE
        });

        Console.WriteLine($"Stack creation initiated. Stack ID: {response.StackId}");
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Error creating stack: {ex.Message}");
    }
}

async Task UpdateStackAsync()
{
    Console.WriteLine("Starting UpdateStackAsync method...");
    try
    {
        Console.WriteLine("Preparing updated template...");
        // Updated template with a modified display name
        string updatedTemplateBody = @"{
          ""Resources"" : {
            ""MySNSTopic"" : {
              ""Type"" : ""AWS::SNS::Topic"",
              ""Properties"" : {
                ""DisplayName"" : ""MySampleTopicUpdated""
              }
            }
          },
          ""Outputs"" : {
            ""TopicARN"" : {
              ""Description"" : ""ARN of the SNS Topic"",
              ""Value"" : { ""Ref"" : ""MySNSTopic"" }
            }
          }
        }";

        Console.WriteLine("Creating UpdateStackRequest...");
        // Create a new request with minimal required parameters
        var request = new UpdateStackRequest
        {
            StackName = "MySNSTopicStack",
            TemplateBody = updatedTemplateBody
        };
        
        Console.WriteLine($"Request details: StackName={request.StackName}, Template length={request.TemplateBody?.Length ?? 0}");
        Console.WriteLine("Calling client.UpdateStackAsync...");
        
        var response = await client.UpdateStackAsync(request);
        
        Console.WriteLine("UpdateStackAsync call completed successfully");
        Console.WriteLine($"Stack update initiated. Stack ID: {response?.StackId ?? "null"}");
    }
    catch (AmazonCloudFormationException ex)
    {
        Console.WriteLine($"CloudFormation error: {ex.Message}");
        Console.WriteLine($"Error code: {ex.ErrorCode}, Request ID: {ex.RequestId}");
        Console.WriteLine($"Status code: {ex.StatusCode}");
        
        if (ex.Message.Contains("No updates are to be performed"))
        {
            Console.WriteLine("No updates needed for the stack.");
        }
    }
    catch (AmazonServiceException ex)
    {
        Console.WriteLine($"AWS Service error: {ex.Message}");
        Console.WriteLine($"Error type: {ex.ErrorType}, Error code: {ex.ErrorCode}");
        Console.WriteLine($"Request ID: {ex.RequestId}, Status code: {ex.StatusCode}");
    }
    catch (Exception ex)
    {
        Console.WriteLine($"Error updating stack: {ex.Message}");
        Console.WriteLine($"Error type: {ex.GetType().FullName}");
        Console.WriteLine($"Stack trace: {ex.StackTrace}");
        
        if (ex.InnerException != null)
        {
            Console.WriteLine($"Inner exception: {ex.InnerException.Message}");
            Console.WriteLine($"Inner exception type: {ex.InnerException.GetType().FullName}");
        }
    }
    Console.WriteLine("UpdateStackAsync method completed.");
}

dotnet build
dotnet run  

Hello, World!
Starting UpdateStackAsync method...
Preparing updated template...
Creating UpdateStackRequest...
Request details: StackName=MySNSTopicStack, Template length=417
Calling client.UpdateStackAsync...
Error updating stack: Object reference not set to an instance of an object.
Error type: System.NullReferenceException
Stack trace:    at Amazon.CloudFormation.Internal.ProcessRequestHandler.PreInvoke(IExecutionContext executionContext)
   at Amazon.CloudFormation.Internal.ProcessRequestHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.PipelineHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.BaseEndpointResolver.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.PipelineHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.BaseAuthResolverHandler.<>n__0[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.BaseAuthResolverHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.CallbackHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.ErrorCallbackHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Amazon.Runtime.Internal.MetricsHandler.InvokeAsync[T](IExecutionContext executionContext)
   at Program.<>c__DisplayClass0_0.<<<Main>$>g__UpdateStackAsync|1>d.MoveNext() in /home/*******/Program.cs:line 96
UpdateStackAsync method completed.

Possible Solution

No response

Additional Information/Context

No response

AWS .NET SDK and/or Package version used

AWSSDK.CloudFormation:4.0.0.4
AWSSDK.Core:4.0.0.5

Targeted .NET Platform

8.0.115

Operating System and version

Ubuntu 24.04.2 LTS

[ashishdhingra]

Reproducible using customer's provided code. Missing null check here.

The fix could be something like below:

...
        /// <summary>
        /// Set NotificationARNs to empty if the collection is empty before continuing on in the pipeline.
        /// </summary>
        /// <param name="executionContext"></param>
        protected virtual void PreInvoke(IExecutionContext executionContext)
        {
            var request = executionContext.RequestContext.Request;
            var updateStackRequest = request.OriginalRequest as UpdateStackRequest;
            if (updateStackRequest != null)
            {
                var arns = updateStackRequest.NotificationARNs;
                bool arnsAutoConstructed = arns is AutoConstructedList<string>;

                // if there are no NotificationARNs and the list was created by user (type is NOT AutoConstructed)
                // only then pass empty param
                if (arns.Count == 0 && !arnsAutoConstructed)
                {
                    if (request.Parameters.ContainsKey("NotificationARNs"))
                    {
                        request.Parameters["NotificationARNs"] = string.Empty;
                    }
                    else
                    {
                        request.Parameters.Add("NotificationARNs", string.Empty);
                    }
                }
            }
        }
...