I tested
BufDataset1.Filter := 'ART_PAK = 10';
This works correctly.
But how to filter out empty values is not clear.
'FieldName Is Null' or 'FieldName = Null' does not work.According to Delphi docs (http://docwiki.embarcadero.com/Libraries/Sydney/en/Data.DB.TDataSet.Filter) this should work. Therefore, we very probably have a bug here. Please file a bug report. Note that the old bugtracker has been switched off, and issues must be filed on the new gitlab page (link at sidebar, "BugTracker"). Maybe wait for a few days until everything is finished with the move to git.