Swashbuckle.aspnetcore: XML comments NullReferenceException

Created on 25 Mar 2017 · 10Comments · Source: domaindrivendev/Swashbuckle.AspNetCore

First of all, sorry to not send a PR with its test.. I hope you can sniff the problem quickly than I clone the repo and so on.

There is just one method with XML comments.

NullReferenceException: Object reference not set to an instance of an object.
Swashbuckle.AspNetCore.SwaggerGen.XmlCommentsOperationFilter ApplyPropertiesXmlToPropertyParameters
ApiParameterDescription

The API has 2 versions, and all others methods, so far, has no comments.
The whole XML is something like this (I just blurs something)

Company.Feature.Api.txt

Source

fabiomaulo

Most helpful comment

Until the fix is included in a published package, the following should workaround the issue by defaulting any unset model metadata to be the string model.

```c#
public class SwaggerApiDescriptionProvider : IApiDescriptionProvider
{
readonly ModelMetadata @string;

public SwaggerApiDescriptionProvider( IModelMetadataProvider metadadataProvider ) =>
    @string = metadadataProvider.GetMetadataForType( typeof( string ) );

public int Order => 0;

public void OnProvidersExecuted( ApiDescriptionProviderContext context )
{
    foreach ( var result in context.Results )
    {
        foreach ( var parameter in result.ParameterDescriptions )
        {
            if ( parameter.ModelMetadata == null )
            {
                parameter.ModelMetadata = @string;
            }
        }
    }
}

public void OnProvidersExecuting( ApiDescriptionProviderContext context ) { }

}

To wire this up in your application, just use:

```c#
builder.Services.TryAddEnumerable(
  ServiceDescriptor.Transient<IApiDescriptionProvider, SwaggerApiDescriptionProvider>() );

The new API description provider will be run in addition to the built-in provider and fix-up null model metadata before Swagger does it's thing.

I hope that helps.

commonsensesoftware on 29 Mar 2017

👍4

All 10 comments

I'm also facing this, but it seems to have been fixed in #315. Unfortunately, that change is apparently not in RC3.

commonsensesoftware on 28 Mar 2017

It seems that I also meet this problem and I'm using the version 1.0.0-rc3 ,error is as follows:

NullReferenceException: Object reference not set to an instance of an object.
Swashbuckle.AspNetCore.SwaggerGen.XmlCommentsOperationFilter+<>c.<ApplyPropertiesXmlToPropertyParameters>b__11_0(ApiParameterDescription p)

WeihanLi on 29 Mar 2017

Until the fix is included in a published package, the following should workaround the issue by defaulting any unset model metadata to be the string model.

```c#
public class SwaggerApiDescriptionProvider : IApiDescriptionProvider
{
readonly ModelMetadata @string;

public SwaggerApiDescriptionProvider( IModelMetadataProvider metadadataProvider ) =>
    @string = metadadataProvider.GetMetadataForType( typeof( string ) );

public int Order => 0;

public void OnProvidersExecuted( ApiDescriptionProviderContext context )
{
    foreach ( var result in context.Results )
    {
        foreach ( var parameter in result.ParameterDescriptions )
        {
            if ( parameter.ModelMetadata == null )
            {
                parameter.ModelMetadata = @string;
            }
        }
    }
}

public void OnProvidersExecuting( ApiDescriptionProviderContext context ) { }

}

To wire this up in your application, just use:

```c#
builder.Services.TryAddEnumerable(
  ServiceDescriptor.Transient<IApiDescriptionProvider, SwaggerApiDescriptionProvider>() );

The new API description provider will be run in addition to the built-in provider and fix-up null model metadata before Swagger does it's thing.

I hope that helps.

commonsensesoftware on 29 Mar 2017

👍4

When will a new release be available so we don't have to use the work around?

professorjoshua on 13 Apr 2017

@commonsensesoftware I receive an error when I put your code into my application. In the SwaggerApiDescriptionProvider class I get an error on the constructor: "must declare a body because it is not marked abstract, extern, or partial".

Any suggestions?

professorjoshua on 13 Apr 2017

Sounds like a compiler error. If I had to guess, you aren't using C# 7.0 [but should be ;)]. Just change the code from an _expression body_ to an actual body.

commonsensesoftware on 13 Apr 2017

@commonsensesoftware I had figured out the I needed to change the code to an actual body. I have one other issue, no definition of Services within the IConfigurationBuilder (builder). Is this because I'm still using VS2015? Is there another solution for an earlier version of C#?

professorjoshua on 14 Apr 2017

@commonsensesoftware I added:

services.TryAddEnumerable(ServiceDescriptor.Transient());

to the ConfigureServices method. I know see my comments!!!

But I still have an issue because the link to Swagger still fails.

professorjoshua on 14 Apr 2017

Got same issue after updating from rc1 to rc3.

For me, parameter.ModelMetadata always not null so fix does not help.

sm-g on 17 Apr 2017

I believe this was fixed some time ago so going to close it. If you're still experiencing this with the latest version (2.5.0 as of writing), feel free to re-open the issue (with clear repro steps)