CSV Parser not treating ignored values correctly leading to exception

[ghost]

If the generic csv parser encounters a - as value in a column, the data is rejected by:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/intelmq/lib/bot.py", line 978, in process
    events = list(filter(bool, value))
  File "/usr/lib/python3/dist-packages/intelmq/bots/parsers/generic/parser_csv.py", line 130, in parse_line
    raise InvalidValue(key, value)
intelmq.lib.exceptions.InvalidValue: invalid value '-' (<class 'str'>) for key 'extra.cert_orgunit'

Example data is as simple as:

someheader
-

The reason is in these lines of code:

intelmq/intelmq/bots/parsers/generic/parser_csv.py

Lines 129 to 130 in 4d10b2b

	if event.add(key, value, raise_failure=False):
	break

If Message.add gets a value to be ignored (like -), the return value is None, which evaluates to False. I think changing the if-clause to ... is not False is enough.

Please add a testcase for this.