3.6.3 cannot search where customfield IS NULL

Trying to do Status = ‘resolved’ AND TimeWorked > 1 AND ‘CF.{Invoiced}’ IS
’NULL’

now IS NOT works fine but IS NULL returns everything if its null or not!

Any ideas? - I saw that DBIx::SearchBuilder had caused problems in advance
but im using the latest from cpan - im on debian sarge btw

ALSO

reporting on custom transaction fields - any ideas if this is possible if so
how is it done - or can anyone recommend a workaround to getting this data
easily in a search?

Happy new year to you all

Regards

David