how to select null and is not null value from table?

hi all 

i have a product table ...

SELECT TOP 1000 [ProductId]
      ,[IsProduct]
      ,[StoragesRef]
      ,[UnitRef]
      ,[ProductName]
      ,[HasPrice]
      ,[Comment]
  FROM [dbo].[Product]    p

and get this values...

now i want select by this code ...

SELECT * FROM Product   WHERE ProductId=15 AND StoragesRef = 50001 OR Product.StoragesRef  IS NULL

i get this value ...

this value is not normal 

how to solve it 

please help me

thanks

Name of Allah, Most Gracious, Most Merciful and He created the human