code: @CheckForNull
      public Plugin getPlugin(String shortName) {
          PluginWrapper p = pluginManager.getPlugin(shortName);
          if(p==null)     return null;
          return p.getPlugin();
      }
docs: Gets the plugin object from its short name.
  This allows URL {@code hudson/plugin/ID} to be served by the views
  of the plugin class.
  @param shortName Short name of the plugin
  @return The plugin singleton or {@code null} if for some reason the plugin is not loaded.
  The fact the plugin is loaded does not mean it is enabled and fully initialized for the current Jenkins session.
  Use {@link Plugin#getWrapper()} and then {@link PluginWrapper#isActive()} to check it.