Set proper fallbacks for start and end date (#4568)

frappe/desk/calendar.py

@@ -35,9 +35,12 @@ def get_events(doctype, start, end, field_map, filters=None, fields=None):
 	if not fields:
 		fields = [field_map.start, field_map.end, field_map.title, 'name']
 
+	start_date = "ifnull(%s, '0000-00-00 00:00:00')" % field_map.start
+	end_date = "ifnull(%s, '2199-12-31 00:00:00')" % field_map.end
+
 	filters += [
-		[doctype, field_map.start, '<=', end],
-		[doctype, field_map.end, '>=', start],
+		[doctype, start_date, '<=', end],
+		[doctype, end_date, '>=', start],
 	]
 
 	return frappe.get_list(doctype, fields=fields, filters=filters)