Added ability to query for field equal to null
Added ability to query for field equal to null

wgerlach/Shock,MG-RAST/Shock,MG-RAST/Shock,MG-RAST/Shock,teharrison/Shock,teharrison/Shock,wgerlach/Shock,teharrison/Shock,teharrison/Shock,MG-RAST/Shock,teharrison/Shock,wgerlach/Shock,teharrison/Shock,wgerlach/Shock,MG-RAST/Shock,wgerlach/Shock