IIF Statement Is Acting Up In A Query

I have a query which is based on 2 tables (Log2000 & Customers) and criteria is entered by the user via a form called 'SearchMarkets'.

In concept, if the user chooses a 'Market' on this form, the query uses that value, otherwise it runs everything. My SQL looks like this:


SELECT Log2000.[Call ID], Customers.ID
FROM Customers INNER JOIN Log2000 ON Customers.CustomerNumber = Log2000.Customer
WHERE (((Customers.ID)=IIf([Forms]![SearchMarkets]![Market] Is Null,([Customers].[ID]) Like "*",[Forms]![SearchMarkets]![Market])));


For non-null values it works grand but the ([Customers].[ID]) Like "*" part isnt returning anything. However this piece of SQL does work when used on its own like this:

SELECT Log2000.[Call ID], Customers.ID
FROM Customers INNER JOIN Log2000 ON Customers.CustomerNumber = Log2000.Customer
WHERE ((([Customers].[ID]) Like "*"));



Can someone please help me overcome this issue?

Thanks in advance!