Crash on WCartesianChart object using a WAbstractItemModel which contains "empty values"
JWt 3.2.3 allow to create a WAbstractItemModel object which contain "empty values", and basing on it is possible to create the relative WCartesianChart object graph.
Using JWt 3.3.0 if you try to create a WCartesianChart based on a WAbstractModel which contain "empty values" the application crash.
You can see this thing by deleting one value from "Category Chart example" table: http://jwt.emweb.be/jwt-charts/charts
Attached the stamp of the exception