Excluding logical deletes in complex select statement

I'm trying to exclude logically deleted items from my Select query but it is not working.

Here is the SQL I am trying to achieve:

SELECT * FROM CMSPerson
WHERE (PersonLastName LIKE 'smith%' OR PersonFirstName LIKE 'smith%')
AND (Deleted IS NULL OR Deleted = 'False' )  

And Here is my code:

CMSPersonCollection coll = new Select().From("CMSPerson")
.WhereBLOCKED EXPRESSION;

The wildcard queries work but it still returns deleted records. Any help? Thanks.

Edit: Well, it won't let my code through but maybe someone can help me anyway...

any particular reason you allow NULL on that column? does it have a meaning other than FALSE?