Did this help?
If you import games into a PGN database with ChessBase, then these games should not contain any “null moves” if you wish to make use of the database with external programs. That might be, e.g., a PGN reader or annotated games for your own website.
External programs are unable to assimilate these games cleanly. The reason for that: the PGN specification does not allow a “null move” in its rules. We include for this a "--". The problem is that in this case what will appear in the PGN notation will be two consecutive moves for the same colour.