Hi!

your GetDisplayText function MUST start equivalent to this:

begin
if AString<>'' then
Exit;

That way, all fields with values will be always correct! All you have to do
now is tell empty fields from null fields. If this is always identical, i.e.
empty string = NULL, then your whole function would be:

begin
if AString='' then
AString:='<null>';
end;

Cheers,
Tobias