Selecting a SDR as a sink

[David Cherkus]

Asked this on chat, thought it might need a broader audience so am asking here 
too...

Part of my flowgraph looks like:





I.e. a selector that selects between output to null sink, osmocom sink or 
PlutoSDR sink.

Problem is when I run the flow and no SDR is present (I select Null Sink by 
default) the code still tries to instantiate the osmocom Sink and that fails.  
If I disable the sinks for radios that aren't present with the 'D' key, then 
the selector complains that the output is no longer connected.  Any ideas how 
to work around this?

Regards,Dave, N1AI