code: @SuppressWarnings("unchecked")
      protected void addPostRunDependent(Executable<? extends Indexable> executable) {
          TaskGroup.HasTaskGroup dependency = (TaskGroup.HasTaskGroup) executable;
          this.addPostRunDependent(dependency);
      }
docs: Add an executable "post-run" dependent for this model.
  
  @param executable the executable "post-run" dependent
  @return the key to be used as parameter to taskResult(string) method to retrieve result of executing
  the executable "post-run" dependent