unmarshall exception

Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `org.jbpm.document.Document` (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
 at [Source: (String)"{
  "myDocuments" : {
  "org.jbpm.document.Documents" : {
    "documents" : [ {
      "org.jbpm.document.service.impl.DocumentImpl" : {
        "identifier" : "b553165a-d6df-4cb6-bf10-e2ad53644fcd",
        "name" : "firstDocument",
        "link" : "",
        "size" : 0,
        "lastModified" : null,
        "content" : "aGVsbG8gZmlyc3QgZG9jdW1lbnQ=",
        "attributes" : {
          "_UPDATED_" : "true"
        }
      }
    }, {
      "org.jbpm.document.service.impl.DocumentImpl" : {
    "[truncated 306 chars]; line: 4, column: 21] (through reference chain: java.util.LinkedHashMap["myDocuments"]->org.jbpm.document.Documents["documents"]->java.util.ArrayList[0])
	at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
	at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1451)
	at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1027)
	at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:265)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:286)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:245)
	at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:27)
	at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:136)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:288)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:151)
	at org.kie.server.api.marshalling.json.JSONMarshaller$CustomAsWrapperTypeDeserializer.deserializeTypedFromObject(JSONMarshaller.java:804)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeWithType(BeanDeserializerBase.java:1171)
	at com.fasterxml.jackson.databind.deser.impl.TypeWrappedDeserializer.deserialize(TypeWrappedDeserializer.java:68)
	at com.fasterxml.jackson.databind.ObjectMapper._readValue(ObjectMapper.java:3972)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2264)
	at org.kie.server.api.marshalling.json.JSONMarshaller$CustomObjectDeserializer.mapObject(JSONMarshaller.java:672)
	at com.fasterxml.jackson.databind.deser.std.UntypedObjectDeserializer.deserialize(UntypedObjectDeserializer.java:248)
	at com.fasterxml.jackson.databind.deser.std.MapDeserializer._readAndBindStringKeyMap(MapDeserializer.java:527)
	at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:364)
	at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:29)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2992)
	at org.kie.server.api.marshalling.json.JSONMarshaller.unmarshall(JSONMarshaller.java:289)
	... 70 more