py3: make thresholds take None for an answer
py3: make thresholds take None for an answer

valdur55/py3status,Andrwe/py3status,ultrabug/py3status,Andrwe/py3status,guiniol/py3status,valdur55/py3status,valdur55/py3status,tobes/py3status,tobes/py3status,ultrabug/py3status,ultrabug/py3status,guiniol/py3status