well we had another bug because we were not doing this in a strong typed way. this https://github.com/Particular/NServiceBus/blob/develop/src/NServiceBus.Core/Unicast/Behaviors/CallbackInvocationBehavior.cs#L60  was returning null since the type was not `IEnumerable<LogicalMessage>`. This highlights my concern about an un-typed dictionary.

And it is not misleading since previously it was in the dictionary anyway.