quickform exportValues never returns null ?

Hi,

It seems that exportValues never returns null for text inputs, even when
no value was entered. That's not such a bit deal, I thought I can
overcome this by writing a filter:

function emptyStringsToNull($value)
{
return ($value == '') ? null : $value;
}

But after running that, exportValues still doesn't return nulls, only
empty strings ('');
Is this normal behaviour? Should I just run the filter over the
exportValues to get nulls instead of empty strings?

Thanks!

Jeroen