Default guest_name to '<No Guest>'

custom_components/room_cal_ha/models.py

@@ -7,7 +7,7 @@ from typing import Any
 
 @dataclass
 class ReservationData:
-  guest_name: str | None = None
+  guest_name: str | None = "<No Guest>"
   check_in_date: date | None = None
   check_in_time: time | None = time(14, 0)
   check_out_date: date | None = None