C# – Error while executing test, if using CreateResponse extention method to return Azure Function HttpResonseMessage

My Azure Function code is like below

public static class MyHttpTriggerFunction
{       
    public static async Task<HttpResponseMessage> Run([HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)]HttpRequestMessage req, TraceWriter log)
    {
        // some business logic

        if (valid)
        {
            return req.CreateResponse(HttpStatusCode.OK, true);
        }
        else
        {
             return req.CreateResponse(HttpStatusCode.BadRequest, "some error message");
        }            
    }
}

In my test project I am reading the result like below:

var result = await MyHttpTriggerFunction.Run(req, log).ConfigureAwait(false);

After executing the function, when it try to return the response in result variable, the test method fails with exception.

**

System.InvalidOperationException: The request does not have an
associated configuration object or the provided configuration was
null.

**

I have made sure that test project has the same System.Net.Http.HttpRequestMessageExtension dll.

If I change the function code not to use CreateResponse extension method (this extension method is from the VS 2017 template's code )
and return the response like below, I get the response in test method and the test case runs fine.

var res = new HttpResponseMessage();
if (valid)
{
    res.StatusCode = HttpStatusCode.OK;
    res.Content = new ObjectContent<bool>(true, new JsonMediaTypeFormatter());        
    return res;
}
else
{
     res.StatusCode = HttpStatusCode.BadRequest;
     res.Content = new ObjectContent<string>("some error message", new JsonMediaTypeFormatter());
     return res;
}

Below is the stacktrace of error

Result StackTrace: at
System.Net.Http.HttpRequestMessageExtensions.CreateResponse[T](HttpRequestMessage
request, HttpStatusCode statusCode, T value, HttpConfiguration
configuration) at
System.Net.Http.HttpRequestMessageExtensions.CreateResponse[T](HttpRequestMessage
request, HttpStatusCode statusCode, T value) at
MyFunctionApp.MyHttpTriggerFunction.d__1.MoveNext()
— End of stack trace from previous location where exception was thrown — at
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task
task) at
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task
task) at
System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
at
MyFunctionAppUnitTest.MyHttpTriggerFunctionTest.d__2.MoveNext()
in
C:\Users\rsingh\Desktop\Git_Workspace\ActivationAPI\MyFunctionAppUnitTest\MyHttpTriggerFunctionTest.cs:line
53
— End of stack trace from previous location where exception was thrown — at
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task
task) at
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task
task) at
Microsoft.VisualStudio.TestPlatform.MSTestAdapter.PlatformServices.ThreadOperations.ExecuteWithAbortSafety(Action
action) Result Message: Test method
MyFunctionAppUnitTest.MyHttpTriggerFunctionTest.MyHttpTriggerFunction_SuccessResult
threw exception: System.InvalidOperationException: The request does
not have an associated configuration object or the provided
configuration was null.

Am I missing something trivial