MySQL SELECT query with CASE or IF

I have a table with products priorities per market and in case a market is not defined a default priority with market = NULL. For example:

market - product_id - priority NULL - 101 - 1 NULL - 201 - 2 NULL - 103 - 3 DE - 101 - 2 DE - 103 - 1 DE - 201 - 3 US - 101 - 1 US - 103 - 2

I need a query which gives me all product priorities for a given market but in case this market is not defined in the table then the default values with market = null. When I use WHERE market = 'DE' OR market IS NULL I get both, the entries for DE and NULL, but how to use the WHERE clause to get only DE if it is configured?

Thank you very much for any help!