[Bug]: ApiDescriptionProvider throws Exception

[stefannikolei]

Describe the bug

I have this ApiDescriptionProvider

nternal class ImageSharpApiDescriptionProvider : IApiDescriptionProvider
{
    public int Order => -1000;

    public void OnProvidersExecuted(ApiDescriptionProviderContext context)
    {
        // nothing
    }

    public void OnProvidersExecuting(ApiDescriptionProviderContext context)
    {
        var apiDescriptionCatalog = new ApiDescription
        {
            HttpMethod = "GET",
            ActionDescriptor = new ActionDescriptor
            {
                RouteValues = new Dictionary<string, string?>
                {
                    // Swagger uses this to group endpoints together.
                    // Group methods together using the service name.
                    ["controller"] = "Catalog",
                },
                DisplayName = "Get image",
            },

            RelativePath = "api/v1/Images/{image}",
            GroupName = "v1",
        };

        AddMediaTypeAndParameters(apiDescriptionCatalog);
        context.Results.Add(apiDescriptionCatalog);
    }

    private static void AddMediaTypeAndParameters(ApiDescription apiDescription)
    {
        apiDescription.SupportedRequestFormats.Add(new ApiRequestFormat { MediaType = "application/json" });

        apiDescription.ParameterDescriptions.Add(
            new ApiParameterDescription
            {
                Name = "image",
                Source = BindingSource.Path,
                DefaultValue = string.Empty,
            }
        );

        apiDescription.ParameterDescriptions.Add(
            new ApiParameterDescription
            {
                Name = "width",
                Source = BindingSource.Query,
                DefaultValue = string.Empty,
                Type = typeof(int),
            }
        );
    }
}

This code does not work with the latest Version 7.3

When i remove the parameter which has BindingSource.Query --> no exception is thrown

Expected behavior

Exception is thrown:

Swashbuckle.AspNetCore.SwaggerGen.SwaggerGeneratorException: Failed to generate Operation for action - Get image. See inner exception
 ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetParameterStyle(Type type, BindingSource source)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateParameterWithoutFilter(ApiParameterDescription apiParameter, SchemaRepository schemaRepository)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateParameterAndContext(ApiParameterDescription apiParameter, SchemaRepository schemaRepository)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateParameterAsync(ApiParameterDescription apiParameter, SchemaRepository schemaRepository)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateParametersAsync(ApiDescription apiDescription, SchemaRepository schemaRespository, Func`3 parameterGenerator)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateParametersAsync(ApiDescription apiDescription, SchemaRepository schemaRespository)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationAsync(ApiDescription apiDescription, SchemaRepository schemaRepository, Func`3 parametersGenerator, Func`3 bodyGenerator, Func`3 applyFilters)
   --- End of inner exception stack trace ---
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationAsync(ApiDescription apiDescription, SchemaRepository schemaRepository, Func`3 parametersGenerator, Func`3 bodyGenerator, Func`3 applyFilters)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationAsync(ApiDescription apiDescription, SchemaRepository schemaRepository)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationsAsync(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GeneratePathsAsync(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository, Func`3 operationsGenerator)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GeneratePathsAsync(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository)
   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwaggerAsync(String documentName, String host, String basePath)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|7_0(Endpoint endpoint, Task requestTask, ILogger logger)

Actual behavior

No Exception :)

Steps to reproduce

No response

Exception(s) (if any)

No response

Swashbuckle.AspNetCore version

No response

.NET Version

No response

Anything else?

No response

[martincostello]

What version of Swashbuckle are you using?

[martincostello]

@EvgeniyZ This might be a regression caused by the changes in #3241.

I think there needs to be a null guard on type:

Swashbuckle.AspNetCore/src/Swashbuckle.AspNetCore.SwaggerGen/SwaggerGenerator/SwaggerGenerator.cs

Lines 612 to 618 in 877b43c

	private static ParameterStyle? GetParameterStyle(Type type, BindingSource source)
	{
	return source == BindingSource.Query && type.IsGenericType &&
	typeof(IEnumerable<KeyValuePair<string, string>>).IsAssignableFrom(type)
	? ParameterStyle.DeepObject
	: null;
	}

[stefannikolei]

What version of Swashbuckle are you using?

Atm 7.2 exception occurs on 7.3

[martincostello]

Thanks - in that case it sounds like the bug was introduced by #3241.

[EvgeniyZ]

@martincostello thanks for tagging me, opened PR, please take a look when you can

[martincostello]

@stefannikolei Thanks for reporting this issue - it should be fixed in v7.3.1 which is now available from NuGet.org.