How to use the Null value in a Parameter?

I have a query that uses a parameter that includes NULL values.  Part of my code is this...

WHERE
COREQ_CC_STATUS =@COREQ_CC_STATUS

I populate available values with...

SELECT COREQ_CC_STATUS
FROM [dbo].[COREQ]
GROUP BY COREQ_CC_STATUS
ORDER BY COREQ_CC_STATUS

...but I require the NULL values as well.

In my Report Parameter Properties for @COREQ_CC_STATUS I have "Allow Null Value" checked but when I run the report, I don't see any data when the criteria is NULL.  I see all other data when @COREQ_CC_STATUS is not NULL.  I have tried using...

(COREQ_CC_STATUS =@COREQ_CC_STATUS OR  COREQ_CC_STATUS IS NULL)

..but it gives me non NULL values as well as NULL values.

SO, my question is, how can I change my script to be to include all @COREQ_CC_STATUS options but also be able to isolate each individual value including NULL?