Check for null property value; added typecheck for signal_array.
Check for null property value; added typecheck for signal_array.

malloch/libmapper,libmapper/libmapper,malloch/libmapper,radarsat1/libmapper,malloch/libmapper,malloch/libmapper,malloch/libmapper,radarsat1/libmapper,libmapper/libmapper,radarsat1/libmapper,malloch/libmapper,radarsat1/libmapper,libmapper/libmapper,libmapper/libmapper,libmapper/libmapper,libmapper/libmapper,radarsat1/libmapper