You may have a custom field on all licenses called “isImportant”, which can be set to true or false, or it can be “blank” (doesn't exist or is not defined) - you want to know if you can create a filter when you create a new segment that match that property.
A query for all companies where "licenses.custom.isImportnat is equal to False”, will only match documents where it is exactly False. So any License with this custom parameter undefined will not match.
If you’d like to find all companies with a license that has the parameter either set explicitly to False OR it is not defined (i.e excluding where not explicitly set to True) simply change the segment rule/condition to
"licenses.custom.isImportnat is not equal to True"