The error message showed after execute a global command, and the stack trace is
org.zkoss.zk.ui.impl.UiEngineImpl handleError:1345
>>java.lang.ClassCastException: result of expression '${prodVM.pictureCoverter}' is not a Converter, is null
>> at org.zkoss.bind.impl.PropertyBindingImpl.getConverter(PropertyBindingImpl.java:91)
>> at org.zkoss.bind.impl.LoadPropertyBindingImpl.load(LoadPropertyBindingImpl.java:58)
>> at org.zkoss.bind.impl.BinderImpl.loadOnPropertyChange(BinderImpl.java:338)
>> at org.zkoss.bind.impl.BinderImpl.access$0(BinderImpl.java:323)
>> at org.zkoss.bind.impl.BinderImpl$QueueListener.onEvent(BinderImpl.java:228)
>> at org.zkoss.zk.ui.event.impl.DesktopEventQueue$QueueListener.onEvent(DesktopEventQueue.java:145)
>> at org.zkoss.zk.ui.AbstractComponent.onEvent(AbstractComponent.java:2739)
>> at org.zkoss.zk.ui.AbstractComponent.service(AbstractComponent.java:2710)