Channel Faulted exception on service call when operation returns n

I have a operation contract
Stream GetLogs()

If I return null for some reason on the service side, the client gets a
channel faulted exception - "The communication object,
System.ServiceModel.Channels.ServiceChannel, cannot be used for communication
because it is in the Faulted state.". Any ideas if I need to specify
something in config file? I am using WSDualHttpBinding binding. If I return a
valid stream object, I ndon't see this exception