Stunner - (Un)Marshaller tests for Rest Service Tasks are failing

(Un)Marshaller tests for Rest Service Tasks are failing (https://github.com/kiegroup/kie-wb-common/pull/2091).

1. There are different values before and after marshalling:

   nodeBeforeMarshalling -> executionSet -> taskName -> value = "Rest"
   
   nodeAfterMarshalling -> executionSet -> taskName -> value = "Task"
   

2. If documentation property is not set (it is set to empty value), empty String "" in tests is expected, but actual value is null.
   Note, that currently tests are not failing on documentation property because they are failing on different name first. See comment in JBPM-7072.