use map instead for on creating hash tables

lib/calcms/studio_timeslot_schedule.pm

@@ -20,11 +20,7 @@ sub get_columns($) {
 
 	my $dbh     = db::connect($config);
 	my $cols    = db::get_columns( $dbh, 'calcms_studio_timeslot_schedule' );
-	my $columns = {};
-	for my $col (@$cols) {
-		$columns->{$col} = 1;
-	}
-	return $columns;
+    return { map { $_ => undef } @$cols };
 }
 
 #map schedule id to id