We can't set a null correlation

Otherwise we get a lovely error from Rabbit.Client:
 	mscorlib.dll!System.Text.Encoding.GetBytes(string s) + 0x8b bytes
 	RabbitMQ.Client.dll!RabbitMQ.Client.Impl.WireFormatting.WriteShortstr(RabbitMQ.Util.NetworkBinaryWriter writer, string val) + 0x4c bytes
 	RabbitMQ.Client.dll!RabbitMQ.Client.Impl.ContentHeaderPropertyWriter.WriteShortstr(string val) + 0x28 bytes
>	RabbitMQ.Client.dll!RabbitMQ.Client.Framing.v0_9_1.BasicProperties.WritePropertiesTo(RabbitMQ.Client.Impl.ContentHeaderPropertyWriter writer) + 0x1bf bytes
 	RabbitMQ.Client.dll!RabbitMQ.Client.Impl.ContentHeaderBase.WriteTo(RabbitMQ.Util.NetworkBinaryWriter writer, ulong bodySize) + 0x64 bytes
 	RabbitMQ.Client.dll!RabbitMQ.Client.Impl.Command.Transmit(int channelNumber, RabbitMQ.Client.Impl.ConnectionBase connection) + 0x1de bytes
 	RabbitMQ.Client.dll!RabbitMQ.Client.Impl.SessionBase.Transmit(RabbitMQ.Client.Impl.Command cmd) + 0xb2 bytes
 	RabbitMQ.Client.dll!RabbitMQ.Client.Impl.ModelBase.ModelSend(RabbitMQ.Client.Impl.MethodBase method, RabbitMQ.Client.Impl.ContentHeaderBase header, byte[] body) + 0x9b bytes
 	RabbitMQ.Client.dll!RabbitMQ.Client.Framing.Impl.v0_9_1.Model._Private_BasicPublish(string exchange, string routingKey, bool mandatory, bool immediate, RabbitMQ.Client.IBasicProperties basicProperties, byte[] body) + 0xa5 bytes
 	RabbitMQ.Client.dll!RabbitMQ.Client.Impl.ModelBase.BasicPublish(string exchange, string routingKey, bool mandatory, bool immediate, RabbitMQ.Client.IBasicProperties basicProperties, byte[] body) + 0xdb bytes
 	NServiceBus.Transports.RabbitMQ.dll!NServiceBus.Transports.RabbitMQ.Routing.ConventionalRoutingTopology.Send(RabbitMQ.Client.IModel channel, NServiceBus.Address address, NServiceBus.TransportMessage message, RabbitMQ.Client.IBasicProperties properties) Line 60 + 0x50 bytes	C#
 	NServiceBus.Transports.RabbitMQ.dll!NServiceBus.Transports.RabbitMQ.RabbitMqMessageSender.Send.AnonymousMethod__0(RabbitMQ.Client.IModel channel) Line 13 + 0x29 bytes	C#
 	NServiceBus.Transports.RabbitMQ.dll!NServiceBus.Transports.RabbitMQ.RabbitMqUnitOfWork.ExecuteRabbitMqActions(System.Collections.Generic.IList<System.Action<RabbitMQ.Client.IModel>> actions) Line 86 + 0xe bytes	C#
 	NServiceBus.Transports.RabbitMQ.dll!NServiceBus.Transports.RabbitMQ.RabbitMqUnitOfWork.Add(System.Action<RabbitMQ.Client.IModel> action) Line 32 + 0x42 bytes	C#
 	NServiceBus.Transports.RabbitMQ.dll!NServiceBus.Transports.RabbitMQ.RabbitMqMessageSender.Send(NServiceBus.TransportMessage message, NServiceBus.Address address) Line 10 + 0x36 bytes	C#
 	NServiceBus.Core.dll!NServiceBus.Unicast.Behaviors.DispatchMessageToTransportBehavior.Invoke(NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext context, System.Action next) + 0x639 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext>.InvokeNext(NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext context) + 0x1b1 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext>.InvokeNext.AnonymousMethod__0() + 0x26 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.MessageMutator.MutateOutgoingPhysicalMessageBehavior.Invoke(NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext context, System.Action next) + 0x178 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext>.InvokeNext(NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext context) + 0x1b1 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext>.InvokeNext.AnonymousMethod__0() + 0x26 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Unicast.Behaviors.SerializeMessagesBehavior.Invoke(NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext context, System.Action next) + 0x21f bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext>.InvokeNext(NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext context) + 0x1b1 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext>.Invoke(NServiceBus.Pipeline.Contexts.SendPhysicalMessageContext context) + 0x26 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.PipelineFactory.InvokeSendPipeline(NServiceBus.Unicast.SendOptions sendOptions, NServiceBus.TransportMessage physicalMessage) + 0xcc bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Unicast.Behaviors.CreatePhysicalMessageBehavior.Invoke(NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext context, System.Action next) + 0x371 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext>.InvokeNext(NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext context) + 0x1b1 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext>.InvokeNext.AnonymousMethod__0() + 0x26 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Unicast.Behaviors.MultiMessageBehavior.Invoke(NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext context, System.Action next) + 0xde bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext>.InvokeNext(NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext context) + 0x1b1 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext>.InvokeNext.AnonymousMethod__0() + 0x26 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Unicast.Behaviors.MultiSendValidatorBehavior.Invoke(NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext context, System.Action next) + 0x18e bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext>.InvokeNext(NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext context) + 0x1b1 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.BehaviorChain<NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext>.Invoke(NServiceBus.Pipeline.Contexts.SendLogicalMessagesContext context) + 0x26 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Pipeline.PipelineFactory.InvokeSendPipeline(NServiceBus.Unicast.SendOptions sendOptions, System.Collections.Generic.IEnumerable<NServiceBus.Unicast.Messages.LogicalMessage> messages) + 0xd3 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Unicast.UnicastBus.SendMessages(NServiceBus.Unicast.SendOptions sendOptions, System.Collections.Generic.IEnumerable<NServiceBus.Unicast.Messages.LogicalMessage> messages) + 0x53 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Unicast.UnicastBus.Send(object[] messages) + 0x99 bytes	Unknown
 	NServiceBus.Core.dll!NServiceBus.Unicast.UnicastBus.Send(object message) + 0x69 bytes	Unknown
 	VideoStore.ECommerce.dll!VideoStore.ECommerce.Handlers.OrdersHub.PlaceOrder(string[] videoIds) Line 44 + 0x1a bytes	C#
 	[Native to Managed Transition]
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.Hubs.HubDispatcher.Incoming(Microsoft.AspNet.SignalR.Hubs.IHubIncomingInvokerContext context) + 0xf5 bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.Hubs.AuthorizeModule.BuildIncoming.AnonymousMethod__28(Microsoft.AspNet.SignalR.Hubs.IHubIncomingInvokerContext context) + 0x319 bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.Hubs.HubPipelineModule.BuildIncoming.AnonymousMethod__0(Microsoft.AspNet.SignalR.Hubs.IHubIncomingInvokerContext context) + 0xb2 bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.Hubs.HubPipeline.Invoke(Microsoft.AspNet.SignalR.Hubs.IHubIncomingInvokerContext context) + 0x3e bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.Hubs.HubDispatcher.InvokeHubPipeline(Microsoft.AspNet.SignalR.Hubs.IHub hub, Microsoft.AspNet.SignalR.Json.IJsonValue[] parameterValues, Microsoft.AspNet.SignalR.Hubs.MethodDescriptor methodDescriptor, Microsoft.AspNet.SignalR.Hubs.HubRequest hubRequest, Microsoft.AspNet.SignalR.Hubs.StateChangeTracker tracker) + 0xe6 bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.Hubs.HubDispatcher.OnReceived(Microsoft.AspNet.SignalR.IRequest request, string connectionId, string data) + 0x3f7 bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.PersistentConnection.ProcessRequest.AnonymousMethod__7() + 0x61 bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.TaskAsyncHelper.FromMethod.AnonymousMethod__3b() + 0x2a bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.TaskAsyncHelper.FromMethod<System.Threading.Tasks.Task>(System.Func<System.Threading.Tasks.Task> func) + 0x44 bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.TaskAsyncHelper.FromMethod(System.Func<System.Threading.Tasks.Task> func) + 0x80 bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.PersistentConnection.ProcessRequest.AnonymousMethod__6(string data) + 0xe3 bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.Transports.ForeverTransport.ProcessSendRequest() + 0x97 bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.Transports.ForeverTransport.ProcessRequestCore(Microsoft.AspNet.SignalR.Transports.ITransportConnection connection) + 0xad bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.Transports.ForeverTransport.ProcessRequest(Microsoft.AspNet.SignalR.Transports.ITransportConnection connection) + 0x2b bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.PersistentConnection.ProcessRequest(Microsoft.AspNet.SignalR.Hosting.HostContext context) + 0x5cf bytes
 	Microsoft.AspNet.SignalR.Core.dll!Microsoft.AspNet.SignalR.Hubs.HubDispatcher.ProcessRequest(Microsoft.AspNet.SignalR.Hosting.HostContext context) + 0x1c3 bytes
 	Microsoft.AspNet.SignalR.Owin.dll!Microsoft.AspNet.SignalR.Owin.CallHandler.Invoke(System.Collections.Generic.IDictionary<string,object> environment) + 0x4aa bytes
 	Microsoft.AspNet.SignalR.Owin.dll!Microsoft.AspNet.SignalR.Owin.Handlers.HubDispatcherHandler.Invoke(System.Collections.Generic.IDictionary<string,object> environment) + 0xef bytes
 	Microsoft.Owin.Host.SystemWeb.dll!Microsoft.Owin.Host.SystemWeb.OwinCallContext.Execute() + 0x78 bytes
 	Microsoft.Owin.Host.SystemWeb.dll!Microsoft.Owin.Host.SystemWeb.OwinHttpHandler.BeginProcessRequest(System.Web.HttpContextBase httpContext, System.AsyncCallback callback, object extraData) + 0x1c9 bytes
 	Microsoft.Owin.Host.SystemWeb.dll!Microsoft.Owin.Host.SystemWeb.OwinHttpHandler.System.Web.IHttpAsyncHandler.BeginProcessRequest(System.Web.HttpContext context, System.AsyncCallback cb, object extraData) + 0x4c bytes
 	System.Web.dll!System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() + 0x227 bytes
 	System.Web.dll!System.Web.HttpApplication.ExecuteStep(System.Web.HttpApplication.IExecutionStep step, ref bool completedSynchronously) + 0x9c bytes
 	System.Web.dll!System.Web.HttpApplication.PipelineStepManager.ResumeSteps(System.Exception error) + 0x43d bytes
 	System.Web.dll!System.Web.HttpApplication.BeginProcessRequestNotification(System.Web.HttpContext context, System.AsyncCallback cb) + 0x60 bytes
 	System.Web.dll!System.Web.HttpRuntime.ProcessRequestNotificationPrivate(System.Web.Hosting.IIS7WorkerRequest wr, System.Web.HttpContext context) + 0xbb bytes
 	System.Web.dll!System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(System.IntPtr rootedObjectsPointer, System.IntPtr nativeRequestContext, System.IntPtr moduleData, int flags) + 0x2d7 bytes
 	System.Web.dll!System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(System.IntPtr rootedObjectsPointer, System.IntPtr nativeRequestContext, System.IntPtr moduleData, int flags) + 0x1f bytes
 	[Native to Managed Transition]
 	[Managed to Native Transition]
 	System.Web.dll!System.Web.Hosting.PipelineRuntime.ProcessRequestNotificationHelper(System.IntPtr rootedObjectsPointer, System.IntPtr nativeRequestContext, System.IntPtr moduleData, int flags) + 0x456 bytes
 	System.Web.dll!System.Web.Hosting.PipelineRuntime.ProcessRequestNotification(System.IntPtr rootedObjectsPointer, System.IntPtr nativeRequestContext, System.IntPtr moduleData, int flags) + 0x1f bytes
 	[Appdomain Transition]