Null Value In Column In Select Query

Suppose I have added a xyz bit column in mytable. From now onwards new values inserted in mytable will have 0 or 1 in xyz column but the values that were previously stored will have NULL value in xyz column.

Now I want to write a query in which I will not give xyz parameter always like it can be null or value.

select * from mytable
where class='something'
and xyz is null

or

select * from mytable
where class='something'
and xyz = 1

Now how to write same query for both cases.