Hi Ralph (and others reading this),
Another workaround for this scenario which would be potentially easier to use is to include a space after the dash which follows the account.
For example, if you have account 4000 and wish to output the amount for only a 'blank' department, use "4000- " as the account key, with that trailing space character.
Note that this workaround only works for a single account and not a range of accounts (ie "4000:4999- ")