SQL Output bot: SQL syntax error if fields is emty string (default)

[sebix]

By default the parameter "fields" is empty. An empty string.

The code treats this a value and uses it to generate the field name list:

intelmq/intelmq/bots/outputs/sql/output.py

Lines 46 to 49 in 98df0cd

	key_names = self.fields
	if key_names is None:
	key_names = event.keys()
	valid_keys = [key for key in key_names if key in event]

Instead, empty string should be treated the same as none/null