Who are the officers involved in cases that are voted as 'No Bill'. List their last name and gender.
voted as 'No Bill' refers to grand_jury_disposition = 'No Bill'
SELECT T2.last_name, T2.gender FROM incidents AS T1 INNER JOIN officers AS T2 ON T1.case_number = T2.case_number WHERE T1.grand_jury_disposition = 'No Bill'