It is possible to have a schedule with gaps where no one is on-call during certain times. If no one is on-call at a certain escalation level, the incident will immediately escalate to the next level of the escalation policy. If no one is on-call on the entire escalation policy, an incident will not be created.
If you try to create a new incident in the web UI on a service where no one is on-call, you will get an error message that the Incident cannot be created. Any trigger events sent to an integration where no one is on-call will not trigger an incident.
If you want an incident to be created, but you do not want anyone to be notified or you do not want noisy notifications for an incident, this can be accomplished by setting up support hours on your service using low-urgency Notification Rules.