// Assignment code (for an existing instance obtained via query)
HashSet<Task> tasks = new HashSet<Task>();
tasks.add(new Task("Some work"));
employee.setTasks(tasks);

// Using the classes below
public class EmployeeListener {
    @PreUpdate
    void onPreUpdate(Object o) {
    }
}

@Entity
@EntityListeners( EmployeeListener.class )
public class Employee {
        @Id
        private String name;
        ...
        @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
        protected Collection<Task> tasks;
}

@Entity
public class Task {
        ...
}

java.lang.ClassCastException: java.util.HashSet cannot be cast to org.hibernate.collection.spi.PersistentCollection
	at org.hibernate.event.internal.FlushVisitor.processCollection(FlushVisitor.java:43)
	at org.hibernate.event.internal.AbstractVisitor.processValue(AbstractVisitor.java:104)
	at org.hibernate.event.internal.AbstractVisitor.processValue(AbstractVisitor.java:65)
	at org.hibernate.event.internal.AbstractVisitor.processEntityPropertyValues(AbstractVisitor.java:59)
	at org.hibernate.event.internal.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:166)
	at org.hibernate.event.internal.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:235)
	at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:94)
	at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:38)
	at org.hibernate.internal.SessionImpl.doFlush(SessionImpl.java:1483)
	at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1469)