ผมใช้ iff แล้วมัน Error Type mismatch: 'iif' ครับ ช่วยแนะนำด้วยครับ

<%
dim CustomerID_h,  field_name_Customer, Values_Customer, CustomerName_h, CustomerID_n, CustomerName_n
CustomerID_h = 1
CustomerName_h = 1
CustomerID_n = 52145
CustomerName_n = "mork"

			 if CustomerID_h = 1 then
                field_name_Customer = field_name_Customer & iif(field_name_Customer ="","",", ") & CustomerID
                Values_Customer = Values_Customer & iif(Values_Customer ="","",", ") & CustomerID_n
			end if
			if CustomerName_h = 1 then
				field_name_Customer = field_name_Customer & iif(field_name_Customer ="","",", ") & CustomerName
                Values_Customer = Values_Customer & iif(Values_Customer ="","",", '") & CustomerName_n & "'"
			end if
			
			response.write "field_name_Customer = " & field_name_Customer & "<br>"
			response.write "Values_Customer = " & Values_Customer & "<br>"			
			response.end

%>