Jeff,
I just did this:
used a table
did a seek for .null. on a table using an index on a (non-null) character field
Got data mismatch error
modified the field structure to allow nulls
Redid the search--no error.
I grant you it wasn't a foreign key.

So, I guess my question is: does your child table's fk allow nulls? Also, the seek you paraphrase would be odd. Is it accurate?

>It does not seem possible to define a VFP database relationship where the child table has "insert restrict" and "nulls allowed" on the foreign key column.
>
>I wish to have a child table INVLIVE where the foreign key column CASE_ID may be null. But if CASE_ID is not null, then it is to be a valid value within the parent CASE table.
>
>When I specify the rule of insert restrict, the generated stored procedure has a line like if seek( lcChildID, pcParentWorkArea) which generates an error of datatype mismatch because lcChildID is NULL. The entire stored procedure does not mention or take into account NULLs.
>
>Is there anyway to modify how VFP generates trigger code besides modifying it after the fact?