Conflict Between Null And '*'

I am using an unbound form (based on VBAUnbound.zip) to enter records into a table. following is an excerpt of the code:
Code:.AddNew .Fields("Catalogue_Code") = Me.txb_ip_cataloguecode .Fields("Base_Metal") = Me.cmb_ip_basemetal .Fields("Paint_Type") = Me.cmb_ip_painttype .Fields("Color_Family") = Me.cmb_ip_colorfamily .Fields("Metallic") = Me.cbx_ip_metallic
In the form, for all fields left blank, the code above places a NULL in the table.

I also have a form to search the same database which uses a following kind of SQL string:
Code:SELECT M_Paint.* FROM M_Paint WHERE M_Paint.[Base_metal] Like '*' AND M_Paint.[Paint_Type] Like '*' AND M_Paint.[Color_Family] Like '*' AND M_Paint.[Metallic] Like '*';
This search does not pick records with any fields with NULL if looking for 'Like '*''... which is obvious.

I have tried replacing NULL with ' "" ' and then the query works but I have to manually do this replacement. I have tried putting ' "" ' as the default value of all the combo boxes to see if that changes anything but have had no luck.

My options are:
- Modify my SQL string to include NULL in the search
- Make sure that a zero length string is added to the fields by default when no value is specified
- Anything else that I cannot think of

I will deeply appreciate help for any of the three options... I am out of clues!
Thanks a lot