code: @SuppressWarnings("deprecation")
      @Override
      public String get(Run<?, ?> run, TaskListener listener) {
          try {
              return new ExpandableMessage(backref).expandAll(run, listener);
          } catch (Exception e) {
              LOG.debug("Can't expand backref, returning as is", e);
              return backref;
          }
      }
docs: Just returns what user entered. Expands env vars and token macro