Eustachio,

> I believe that you will discover that no nulls have been posted.

I agree with Helen here.

> In TDataset, all "empty" fields are made to be zero-equivalent -
> zero in numerics and dates, empty string (#0) in character fields.

I disagree. Values are initialized as null; you can't post a null value
if the field's Required property is set to True. It is my understanding
that the Required property is set automatically by reading the database
when you open the dataset, but this may not always be the case
(updatable views, f. ex.).
When you edit a string field in a data-aware control, it becomes
non-null and stays like that event when you clear it; you need to issue
the Clear method of the field object to set the field to null.
Helen's other suggestions remain valid, but I believe that in this
situation the real problem is that you tend to mix blanks and nulls,
which are completely different beasts for TField and not so much for
data-aware controls.
Hope this helps.
--
____
_/\/ando