Hi Derek, and welcome to the forum.
The solution here lies in creating some calculated fields, one for each field which may have null values, which employ a bit of a trick that's been used around here for a while.
For example if one field is CustomerName, name the field extracted from the flat file, say, PreCustomerName. Now build a CustomerName (character type) calculated field with the expression:
Finally, hide the PreCustomerName field and reposition the CustomerName field within the table as necessary.
No, V9 won't do it without the calculated fields either.
There is one nice ability that may have been introduced in V8 (not sure). You can duplicate existing calculated fields easily and then just revise the field names as necessary. Better than starting from scratch. Especially when, as you say, you have quite a few fields which require this approach.
Glad to hear that it helped. Thanks for the update.