add condition for zero appointment slots

erpnext/crm/doctype/appointment/appointment.py

@@ -28,6 +28,7 @@ class Appointment(Document):
 		number_of_appointments_in_same_slot = frappe.db.count(
 			'Appointment', filters={'scheduled_time': self.scheduled_time})
 		number_of_agents = frappe.db.get_single_value('Appointment Booking Settings', 'number_of_agents')
+		if not number_of_agents == 0:
 			if (number_of_appointments_in_same_slot >= number_of_agents):
 				frappe.throw('Time slot is not available')
 		# Link lead