java.io.NotSerializableException: org.activiti.bpmn.model.BpmnModel

hi
I use redis store processDefinitionCache, My flowable.cfg.xml like this
``

**ShareniuDeploymentCache:**
Jedis jedis=new Jedis("127.0.0.1",6379);
public ProcessDefinitionCacheEntry get(String id) {
Object object = cache.get(id);
if (object !=null) {
jedis.set(id.getBytes(), ObjectToArrayUtils.toByteArray(object));
}
System.out.println(id);
return null;
}
``

error message:
java.io.NotSerializableException: org.activiti.bpmn.model.BpmnModel
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
at com.shareniu.shareniu_activiti6.ch2.ObjectToArrayUtils.toByteArray(ObjectToArrayUtils.java:17)