NullReferenceException in AuthorizationValidationRule when query/mutation/parameter name is invalid #61

public static void AddGraphQLAuth(this IServiceCollection services)
{
    services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();
    services.TryAddSingleton<IAuthorizationEvaluator, AuthorizationEvaluator>();
    services.AddTransient<IValidationRule, AuthorizationValidationRule>();

    services.TryAddSingleton(s =>
    {
        var authSettings = new AuthorizationSettings();

        authSettings.AddPolicy("AdminPolicy", _ => _.RequireClaim("role", "Admin"));

        return authSettings;
    });
}

mutation {
  addDevelper(
    id: "b07b3e4e-ea3c-42fc-9c76-40cbdec25ff5",
    name:"john",
    surname: "smith",
    skills: [ 
        { Name: "C#", Score: 10 }, 
        { Name: "JS", Score: 7 }
        ])
}

{
    "errors": [
        {
            "message": "GraphQL.ExecutionError: Object reference not set to an instance of an object. ---> System.NullReferenceException: Object reference not set to an instance of an object.\r\n   at GraphQL.Authorization.AuthorizationValidationRule.<>c__DisplayClass2_1.<Validate>b__2(ObjectField objectFieldAst)\r\n   at GraphQL.Validation.EnterLeaveListener.GraphQL.Validation.INodeVisitor.Enter(INode node)\r\n   at GraphQL.Validation.BasicVisitor.Visit(INode node)\r\n   at 
[..]
GraphQL.Validation.BasicVisitor.Visit(INode node)\r\n   at GraphQL.Validation.DocumentValidator.Validate(String originalQuery, ISchema schema, Document document, IEnumerable`1 rules, Object userContext, Inputs inputs)\r\n   at GraphQL.DocumentExecuter.ExecuteAsync(ExecutionOptions options)\r\n   --- End of inner exception stack trace ---",
            "extensions": {
                "code": "NULL_REFERENCE"
            }
        }
    ]
}

{
    "errors": [
        {
            "message": "GraphQL.Validation.ValidationError: Cannot query field \"addDevelper\" on type \"Mutation\". Did you mean \"addDeveloper\"?",
            [..]
        }
    ]
}

var argumentType = context.TypeInfo.GetArgument().ResolvedType.GetNamedType() as IComplexGraphType;

var argumentType = context.TypeInfo.GetArgument()?.ResolvedType.GetNamedType() as IComplexGraphType;