code: public UpdateSite.Plugin getUpdateInfo() {
          UpdateCenter uc = Jenkins.getInstance().getUpdateCenter();
          UpdateSite.Plugin p = uc.getPlugin(getShortName(), getVersionNumber());
          if(p!=null && p.isNewerThan(getVersion())) return p;
          return null;
      }
docs: If the plugin has {@link #getUpdateInfo() an update},
  returns the {@link hudson.model.UpdateSite.Plugin} object.
  
  @return
  This method may return null &mdash; for example,
  the user may have installed a plugin locally developed.