MassTransit/MassTransit · error · ArgumentNullException

busFactory

Error message

busFactory

What it means

SetBusFactory requires an IRegistrationBusFactory instance to configure how the bus is constructed from the container. Passing null cannot produce a bus factory, so the standard ArgumentNullException(nameof(busFactory)) is thrown immediately, before any DI registrations are made.

Solutions

1. Pass a concrete IRegistrationBusFactory, e.g. new RegistrationBusFactory(...) or the transport-specific factory from the provider package
2. Check the variable/expression passed for null before calling SetBusFactory
3. Ensure the conditional logic that selects the transport always assigns a factory (throw on the unknown-transport branch instead)

Example fix

// before
IRegistrationBusFactory factory = SelectFactory(config); // may return null
configurator.SetBusFactory(factory);

// after
var factory = SelectFactory(config) ?? throw new InvalidOperationException("No transport configured");
configurator.SetBusFactory(factory);

if (busFactory == null)
    throw new InvalidOperationException("busFactory must be provided before calling SetBusFactory");

IRegistrationBusFactory f = maybeFactory ?? throw new InvalidOperationException("Missing bus factory");

try { configurator.SetBusFactory(factory); }
catch (ArgumentNullException ex) { logger.LogError(ex, "Bus factory was null"); throw; }

When it happens

Trigger: Calling SetBusFactory(null) directly, or calling AddBus with a configure callback chain that ends up passing a null factory expression (e.g. a factory variable not yet initialized) into SetBusFactory.

Common situations: Hosting setups where the bus factory is obtained from configuration or a conditional branch (e.g. choosing RabbitMQ vs in-memory at runtime) and every branch fails to assign a value, so null reaches the call.

Related errors

• Value cannot be null. (Parameter 'configure')
• AddMassTransit() was already called and may only be called…
• An exception occurred during bus creation
• authSettings
• callback

AI-assisted analysis of MassTransit/MassTransit@62ab339afa (2026-09-13). Data as JSON: /api/errors/ea932fd2a6cbb659. Report an issue: GitHub.

Appendix: source

Thrown at src/MassTransit/DependencyInjection/Configuration/ServiceCollectionBusConfigurator.cs:82

        protected ServiceCollectionBusConfigurator(IServiceCollection collection, IContainerRegistrar registrar)
            : base(collection, registrar)
        {
            AddMassTransitComponents(collection);
        }

        protected Func<IBus, RequestTimeout, IClientFactory> CreateClientFactory { get; private set; } = DefaultClientFactory;

        [Obsolete("Use 'Using[TransportName]' instead. Visit https://masstransit.io/obsolete for details.", true)]
        public virtual void AddBus(Func<IBusRegistrationContext, IBusControl> busFactory)
        {
            SetBusFactory(new RegistrationBusFactory(busFactory));
        }

        public virtual void SetBusFactory<T>(T busFactory)
            where T : class, IRegistrationBusFactory
        {
            if (busFactory == null)
                throw new ArgumentNullException(nameof(busFactory));

            ThrowIfAlreadyConfigured(nameof(SetBusFactory));

            this.AddSingleton(provider => Bind<IBus>.Create(CreateBus(busFactory, provider)));

            this.AddSingleton(provider => provider.GetRequiredService<Bind<IBus, IBusInstance>>().Value);
            this.AddSingleton<IReceiveEndpointConnector>(provider => provider.GetRequiredService<Bind<IBus, IBusInstance>>().Value);
            this.AddSingleton(provider => provider.GetRequiredService<Bind<IBus, IBusInstance>>().Value.BusControl);
            this.AddSingleton(provider => provider.GetRequiredService<Bind<IBus, IBusInstance>>().Value.Bus);

            Registrar.RegisterScopedClientFactory();
        }

        public virtual void AddRider(Action<IRiderRegistrationConfigurator> configure)
        {
            var configurator = new ServiceCollectionRiderConfigurator(this, new DependencyInjectionRiderContainerRegistrar<IBus>(this));
            configure?.Invoke(configurator);
        }

View on GitHub (pinned to 62ab339afa)