private function getUpdateChangeSetHandler()
    {
        return function ($key, $value, $obj) {
            $op = '$set';
            if (null === $value) {
                $op = '$unset';
                $value = 1;
            }
            $obj[$op][$key] = $value;
            return $obj;
        };
    }
private function getUpdateChangeSetHandler()
    {
        return function ($key, $value, $obj) {
            $op = '$set';
            if (null === $value) {
                $op = '$unset';
                $value = 1;
            }
            $obj[$op][$key] = $value;
            return $obj;
        };
    }
private function getUpdateChangeSetHandler ( ) { return function ( $ key , $ value , $ obj ) { $ op = '$set' ; if ( null === $ value ) { $ op = '$unset' ; $ value = 1 ; } $ obj [ $ op ] [ $ key ] = $ value ; return $ obj ; } ; }
Gets the change set handler Closure for update.

@return  Closure
Gets the change set handler Closure for update .