NotSerializableException on org.keycloak.services.DefaultKeycloakSession using RH-SSO 7.1 standalone cluster mode with custom User Storage SPI

Issue

• Error in log

  ...
  Caused by: org.infinispan.commons.marshall.NotSerializableException: org.keycloak.services.DefaultKeycloakSession
  Caused by: an exception which occurred:
      in field session
      in field value
      in field instance
      in object java.util.concurrent.ConcurrentHashMap@3769c23c
      in object org.wildfly.clustering.ejb.infinispan.group.InfinispanBeanGroupEntry@65e67da0
      in object org.infinispan.commands.write.PutKeyValueCommand@eeb6ec6e
      in object org.infinispan.commands.tx.PrepareCommand@d8edf297
  ...