code: @SuppressWarnings("unchecked")
      protected String addPostRunDependent(Creatable<? extends Indexable> creatable) {
          TaskGroup.HasTaskGroup dependency = (TaskGroup.HasTaskGroup) creatable;
          return this.addPostRunDependent(dependency);
      }
docs: Add a creatable "post-run" dependent for this task item.
  
  @param creatable the creatable "post-run" dependent.
  @return the key to be used as parameter to taskResult(string) method to retrieve created "post-run" dependent