userTaskService.saveContent does not work in RHPAM 7.8.0

Issue

• userTaskService.saveContent method returns error on RHPAM 7.8.0:

  2020-08-19 17:49:22.449  WARN 82337 --- [pool-4-thread-1] .j.s.t.d.n.i.NotificationListenerManager : Exception encountered while notifying listener com.company.service.SampleListener@43efe064 with event org.kie.internal.task.api.model.NotificationEvent@340155ce - error User 'null' does not have permissions to execute operation 'Modify' on task id 5
  

• Error message User 'null' does not have permissions to execute operation 'Modify' on task id 5 when using userTaskService.saveContent method;