fixed bug when sending an empty list of messages to a null destination.

src/unicast/NServiceBus.Unicast/UnicastBus.cs

@@ -514,13 +514,13 @@ private ICallback SendMessage(string destination, string correlationId, MessageI
                         return null;
             }
 
+            if (messages == null || messages.Length == 0)
+                throw new InvalidOperationException("Cannot send an empty set of messages.");
+
             if (destination == null)
                 throw new InvalidOperationException(
                     string.Format("No destination specified for message {0}. Message cannot be sent. Check the UnicastBusConfig section in your config file and ensure that a MessageEndpointMapping exists for the message type.", messages[0].GetType().FullName));
 
-            if (messages == null || messages.Length == 0)
-                throw new InvalidOperationException("Cannot send an empty set of messages.");
-
             foreach (var id in SendMessage(new List<string> { destination }, correlationId, messageIntent, messages))
             {
                 var result = new Callback(id);