#Error when DateTime field is NULL

 Hi

When Fields!DOM_PORT_DATE.Value is NULL in the database, the report returns #ERROR

is the date is populated, then it outputs Fields!DOM_PORT_DATE.Value minus 10 days , which is correct

=IIF(Fields!ANALYSIS__.Value = "EBK_BOLI", "* BOL Instuctions given to us by: " & IIF(isnothing(Fields!DOM_PORT_DATE.Value),"TBC",DATEADD("d",-10,Fields!DOM_PORT_DATE.Value)), 

How do fix the issue when the date field is NULL??

FYG, if i subsitute Fields!DOM_PORT_DATE.Value with Today , the statement works.

example of Fields!DOM_PORT_DATE.Value

2/3/2013 12:00:00 AM

Please help as been trying to fix this for past 2 hrs!! :(