mysql does not have "ISNULL", replaced with "= NULL"

server.py

@@ -210,7 +210,7 @@ def get_announcements(minlevel=0):
 	offset = timedelta()
 	if ismod():
 		offset = timedelta(hours=24)
-	return query('SELECT * FROM announcements WHERE NOT deleted AND (time_expire ISNULL OR time_expire > ?) AND (? OR (visible AND time_publish < ?)) AND level >= ? ORDER BY level DESC', datetime.now()-offset, ismod(), datetime.now(), minlevel)
+	return query('SELECT * FROM announcements WHERE NOT deleted AND ((time_expire = NULL) OR time_expire > ?) AND (? OR (visible AND time_publish < ?)) AND level >= ? ORDER BY level DESC', datetime.now()-offset, ismod(), datetime.now(), minlevel)
 
 @app.template_filter()
 def fixnl(s):