Handling EDatabaseError afterTTable.post

I created a Paradox table with fields, which require not null values.
When I click on the Navigator on a Delphi-Form in order to insert data
with null values, consequently an EDatabaseError is raised and the
program is stopped by the RTL.
I want to supress this harsh reaction and give the user a chance to
fill the needed values.
If I understand the VCL-Sourcecode, the EDatabaseError-raising
procedure is the CheckRequiredFields-method, which is itself called by
theTDataSet.Post-method.
So I have to get  these calls within a try .. except - block, which is
closer to raise of the EDatabaseError, than the RTL.
How can I do this?

The OnPostError-Event and the BeforePost-Event of the Table are
applied after the call of CheckRequiredFields, so they come too late.

I tried check the fields in the OnUpdate-Event in a try ..  except
block and to raise an EDatabaseError myself, if the value is null -
but this cannot cancel the TDataSet.post-call, which already happened
outside the sheltered area.

In ordinary Pascal I would derive a new component from TTable in order
to control the post-method. But this simple problem must admit a
solution by native Delphi-methods.

Thanks a lot for all helpfull advices.
Tho...@Lauer.in-berlin.de