I have a combo box that has a row source type of fields and the row source is the field name in the database. The database has codes that I want them to pick from. I put in the valid clause:

if this.value != dbf.field
return .f.
else
return .t.
endif

this works fine when I want them to only pick from the database. The problem is sometimes I want to let them put in a blank and still do the validation. So, I tried:

if !empty(this.value) AND this.value != dbf.field
return .f.
else
return .t.
endif

the problem is that if you put in a blank or an invalid code this.value is empty. How do I know if they left the field blank or put in an invalid code?