Why is AWS lambda function getting NullReferenceException in C# API?

Question

I have a .Net 6 API which is deployed on AWS lambda. In theory everything is set up right, but when I try to call the API from postman, it giver "internal server error".

The problem is a NullReferenceException.

2022-12-23T19:59:07.791Z    9b343352-fd3f-4c34-a1a5-3f46251b7f1e    fail    System.NullReferenceException: Object reference not set to an instance of an object.

at Amazon.Lambda.AspNetCoreServer.APIGatewayProxyFunction.MarshallRequest(InvokeFeatures features, APIGatewayProxyRequest apiGatewayRequest, ILambdaContext lambdaContext)

at Amazon.Lambda.AspNetCoreServer.AbstractAspNetCoreFunction`2.FunctionHandlerAsync(TREQUEST request, ILambdaContext lambdaContext)

at lambda_method2(Closure , Stream , ILambdaContext , Stream )

at Amazon.Lambda.RuntimeSupport.Bootstrap.UserCodeLoader.Invoke(Stream lambdaData, ILambdaContext lambdaContext, Stream outStream) in /src/Repo/Libraries/src/Amazon.Lambda.RuntimeSupport/Bootstrap/UserCodeLoader.cs:line 145

at Amazon.Lambda.RuntimeSupport.HandlerWrapper.<>c__DisplayClass8_0.<GetHandlerWrapper>b__0(InvocationRequest invocation) in /src/Repo/Libraries/src/Amazon.Lambda.RuntimeSupport/Bootstrap/HandlerWrapper.cs:line 56

at Amazon.Lambda.RuntimeSupport.LambdaBootstrap.InvokeOnceAsync(CancellationToken cancellationToken) in /src/Repo/Libraries/src/Amazon.Lambda.RuntimeSupport/Bootstrap/LambdaBootstrap.cs:line 176

I call the FunctionHandlerAsync in AWS, which I read is the correct function, I followed many tutorials on how to set it up, but even if I did it in the same way, just doesn't work.

Lambda entrypoint:

namespace API
{
    public class LambdaFunction : Amazon.Lambda.AspNetCoreServer.APIGatewayProxyFunction
    {
        protected override void Init(IWebHostBuilder builder)
        {
            try
            {
                builder.UseContentRoot(Directory.GetCurrentDirectory()).UseStartup<Startup>().UseLambdaServer();
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }
    }
}

Although the request passes, I also get some error when I try to test the API in the lambda test with

{
  "statusCode": 404,
  "headers": {},
  "multiValueHeaders": {
    "Content-Type": [
      null
    ]
  },
  "body": "",
  "isBase64Encoded": false

I am new to this cloud world and I would really need some solution to this, I am working on it for 3 days and literally the deployment generates me a way bigger headache than the actual creation of the API.

`AspNetCoreServer`? Can you please show us your using statements? Which Nuget packages do you have configured? What is your request? — Ermiya Eskandary, Dec 23 '22 at 22:39
Yes, `AspNetCoreServer` is the package. No other using statements in that class, but I post the packages included: I also tried both GET and POST requests, non of them are working — Újfalusi Ábel, Dec 23 '22 at 22:59
404 suggests you're not calling it correctly - how are you calling it? What's your request? — Ermiya Eskandary, Dec 23 '22 at 23:12
I run the lambda test, default API Gateway Proxy test, when I get the 404. When I call it from Postman, Get or Post, I get internal server error 500. — Újfalusi Ábel, Dec 24 '22 at 08:54
Have you been able to figure this out? Hitting the same problem. — Eternal21, Dec 29 '22 at 03:53
Don’t wrap your inner exception. You are loosing stack information — Daniel A. White, Feb 07 '23 at 14:04

Kevin · Answer 1 · 2023-02-07T14:31:53.717

0

My problem for me was function-handler in the aws-lambda-tools-defaults.json file that was not correct because the function that I was trying to deploy was not existing (cause of the NullReferenceException). So just make sure that the path to it is correct.

edited Feb 07 '23 at 14:31

answered Feb 07 '23 at 14:02

Kevin

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Why is AWS lambda function getting NullReferenceException in C# API?

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