update gradesheet sorting function to better handle NaN (#833)
update gradesheet sorting function to better handle NaN (#833)


autolab/Autolab,cg2v/Autolab,cg2v/Autolab,cg2v/Autolab,autolab/Autolab,autolab/Autolab,autolab/Autolab,autolab/Autolab,cg2v/Autolab,cg2v/Autolab,autolab/Autolab,cg2v/Autolab