HangfireIO/Hangfire · error · ArgumentNullException

filterProvider

Error message

filterProvider

What it means

Thrown by the internal BackgroundJobFactory constructor when filterProvider is null. BackgroundJobFactory decorates a CoreBackgroundJobFactory and resolves IClientFilter instances through IJobFilterProvider before job creation. This guard ensures the filter-discovery step (GetFilters -> _filterProvider.GetFilters(job)) never dereferences null. The internal constructor is used by the public constructor that defaults to JobFilterProviders.Providers and wires a StateMachine.

Source

Thrown at src/Hangfire.Core/Client/BackgroundJobFactory.cs:65

                    return factory.RetryAttempts;
                }

                return 0;
            }
            set
            {
                if (_innerFactory is CoreBackgroundJobFactory factory)
                {
                    factory.RetryAttempts = value;
                }
            }
        }

        internal BackgroundJobFactory(
            [NotNull] IJobFilterProvider filterProvider, 
            [NotNull] IBackgroundJobFactory innerFactory)
        {
            if (filterProvider == null) throw new ArgumentNullException(nameof(filterProvider));
            if (innerFactory == null) throw new ArgumentNullException(nameof(innerFactory));

            _filterProvider = filterProvider;
            _innerFactory = innerFactory;
        }

        public IStateMachine StateMachine => _innerFactory.StateMachine;

        public BackgroundJob Create(CreateContext context)
        {
            if (context == null) throw new ArgumentNullException(nameof(context));

            var filterInfo = GetFilters(context.Job);

            try
            {
                context.Factory = this;

View on GitHub (pinned to c236dd0f93)

Solutions

1. Use the parameterless BackgroundJobFactory() constructor or the public one accepting IJobFilterProvider — never the internal constructor.
2. Register a concrete IJobFilterProvider (e.g., JobFilterProviders.Providers) in your DI container.
3. In tests, pass a mock/fake IJobFilterProvider (e.g., new EmptyFilterProvider() or JobFilterProviders.Providers).

Example fix

// before
var factory = new BackgroundJobFactory(null);

// after
var factory = new BackgroundJobFactory(); // uses JobFilterProviders.Providers
// or explicitly:
var factory = new BackgroundJobFactory(JobFilterProviders.Providers);

var provider = filterProvider ?? JobFilterProviders.Providers;
var factory = new BackgroundJobFactory(provider);

public static bool IsValidFilterProvider(IJobFilterProvider p)
    => p != null;

When it happens

Trigger: Calling the internal BackgroundJobFactory(IJobFilterProvider, IBackgroundJobFactory) constructor (via reflection or a friend assembly) with a null filterProvider; a custom IBackgroundJobFactory wrapper that forwards a null provider.

Common situations: Subclassing or wrapping BackgroundJobFactory with dependency injection containers that fail to resolve IJobFilterProvider; test fixtures that pass null instead of JobFilterProviders.Providers or a mock provider.

Related errors

• context
• stateMachine
• activator
• client
• context

AI-assisted analysis of HangfireIO/Hangfire@c236dd0f93 (2026-08-13). Data as JSON: /api/errors/4ab0928ac8d1e90f. Report an issue: GitHub.