Not serializable: org.apache.tapestry5.tree.DefaultTreeExpansionModel - can't persist sessions across cluster

org.apache.tapestry5.tree.DefaultTreeExpansionModel is not serializable but used in a persisted field in the Tree component in tapestry-core.

If you want to persist your sessions to the filesystem or to database (for clustering) the serialization fails. the class contains only serializable values, so this can be fixed with adding the serializable interface to the DefaultTreeExpansionModel

as a quick fix one can extend the DefaultTreeExpansionModel and add the serializable interface and use this class with the Tree component parameter "expansionModel":

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import java.io.Serializable;

import org.apache.tapestry5.tree.DefaultTreeExpansionModel;

public class SerializableTreeExpansionModel<T> extends DefaultTreeExpansionModel<T> implements Serializable

{ private static final long serialVersionUID = 88777116818436263L; }