Make Visualization sink default to NullSink because it might not always be used.
Make Visualization sink default to NullSink because it might not always be used.

jacksonic/vjlofvhjfgm,foam-framework/foam2,foam-framework/foam2,foam-framework/foam2,foam-framework/foam2,foam-framework/foam2,jacksonic/vjlofvhjfgm,jacksonic/vjlofvhjfgm