check that given user_list is a list
check that given user_list is a list

critzo/operator,nkinkade/operator,stephen-soltesz/operator,jheretic/operator,critzo/operator,m-lab/operator,salarcon215/operator,salarcon215/operator,jheretic/operator,nkinkade/operator,m-lab/operator,stephen-soltesz/operator