Following error happens on graph configuration screen.

Undefined index: 24508 [graphs.php:239 ? CAPIObject->update() ? CAPIObject->__call() ? czbxrpc::call() ? czbxrpc::callAPI() ? call_user_func() ? CGraphGeneral->update() ? CGraph->validateUpdate() ? CGraph->validateItems() in /usr/share/zabbix/api/classes/CGraph.php:731]

The cause of this problem is "Y axis MIN/MAX value". The step of reproduce:

1. create new graph
2. add some items (item A and B)
3. select "Item" for Y axis MIN value, and select item A
4. select "Calculted" for Y axis MIN value
5. remove item A from graph items
5. save