fix: unavailability validations

lms/lms/doctype/course_evaluator/course_evaluator.py

@@ -21,7 +21,11 @@ class CourseEvaluator(Document):
 		if self.unavailable_to and not self.unavailable_from:
 			frappe.throw(_("Unavailable From Date is mandatory if Unavailable To Date is set"))
 
-		if self.unavailable_from >= self.unavailable_to:
+		if (
+			self.unavailable_from
+			and self.unavailable_to
+			and self.unavailable_from >= self.unavailable_to
+		):
 			frappe.throw(_("Unavailable From Date cannot be greater than Unavailable To Date"))
 
 	def validate_time_slots(self):