Out of all the incidents of domestic violence reported at the ward represented by alderman Walter Burnett Jr., how many were arrested?
domestic violence refers to domestic = 'TRUE'; arrested refers to arrest = 'TRUE'
SELECT SUM(CASE WHEN T2.arrest = 'TRUE' THEN 1 ELSE 0 END) FROM Ward AS T1 INNER JOIN Crime AS T2 ON T1.ward_no = T2.ward_no WHERE T1.alderman_first_name = 'Walter' AND T1.alderman_last_name = 'Burnett' AND alderman_name_suffix = 'Jr.' AND T2.domestic = 'TRUE'