I have a combobox where it holds list of persons which also includes user objects ,as user extends person.

On onChange event of the combobox it throws :

Caused by: org.zkoss.zel.ELException: Cannot convert PersonDataImpl [id=40] of type class com.symeo.pms.entity.PersonDataImpl to class com.symeo.pms.entity.UserDataImpl
at org.zkoss.zel.impl.lang.ELSupport.coerceToTypeForSetValue(ELSupport.java:490) [zel-7.0.5.jar:7.0.5]
at org.zkoss.zel.impl.parser.AstValue.setValue(AstValue.java:246) [zel-7.0.5.jar:7.0.5]
at org.zkoss.zel.impl.ValueExpressionImpl.setValue(ValueExpressionImpl.java:247) [zel-7.0.5.jar:7.0.5]
at org.zkoss.xel.zel.ELXelExpression.setValue(ELXelExpression.java:50) [zcommon-7.0.5.jar:7.0.5]
at org.zkoss.bind.impl.BindEvaluatorXImpl.setValue(BindEvaluatorXImpl.java:58) [zkbind-7.0.5.jar:7.0.5]
... 45 more

Internally it tries to compare the object type ,though user is subclass of person.

And it happens only when we use a form and bind form attribute i.e "@bind(fx.contact)" where fx is form id,if we directly bind the main object rather then middle form object i.e "@bind(vm.object.contact)" where vm is the view model this issue does not exists .