I have a parameterized view which I then index on:

INDEX ON v_ViewName.cFieldName TAG cFieldName [Character field]
and
INDEX ON v_ViewName.dFieldName TAG dFieldName [DateTime field].

I get the subject error message 'INDEX does not accept NULL'. I find no reference in the documentation, Hacker's Guide, or FoxWiki.

How could I resolve this isssue other than changing the view to substitute blanks / empty DateTime?