Steps to reproduce:
- Navigate to Configuration -> Hosts -> Graphs
- Create a graph and specify some item as Y min value.
- Save changes
- Open same graph for editing
- Delete selected host and item from "Y axis MIN value" field (or type in some invalid value)
- Click "Update"
Message tells that graph is updated. Opening a graph form again, see that changes are not made.
Validation should check if mandatory field is filled.