Query Help with Max function

[CFrockchelle]

Ok Heres the situtation. I need to show a list of customers who have a invoice date that is 2 years or older or they have a last ship date that is 2 years or older. I'm using the max function on the last date ship since there are several shipping dates and I need to get the lastest ship date to see if it is older than 2 years. When I use the max function of course it elimates the null values for the last date ship. The problem with this is that the customer may have a invoice date that is 2 years old or older but have a null last shipped date so therefore that customer is not displayed but I need them to display.Is there another way to write the query to show the null shipping dates?
Here is a generic version of what I have:

Select d.billID,d.cust_id,d.cust_name,d.lastInvoice, d.purged,max(o.dateshipped)
From CustomerData d left join OrderInf o
on d.cust_id = o.cust_id
Where datediff(yyyy,lst_ivcdat,getdate()) > 2
or purged = 'y'
group by d.billID,d.cust_id,d.cust_name,d.lastInvoice,
d.purged
having datediff(yyyy,max(dt_lst_shp),getdate()) > 2


Thanks in Advance for any help!!!