public function PreviewTheme($ThemeName = '') {
      $this->Permission('Garden.Settings.Manage');
      $ThemeInfo = Gdn::ThemeManager()->GetThemeInfo($ThemeName);
      
      $PreviewThemeName = $ThemeName;
      $PreviewThemeFolder = GetValue('Folder', $ThemeInfo);
      
      // If we failed to get the requested theme, cancel preview
      if ($ThemeInfo === FALSE) {
         $PreviewThemeName = '';
         $PreviewThemeFolder = '';
      }
      
      Gdn::Session()->SetPreference(array('PreviewThemeName' => $PreviewThemeName, 'PreviewThemeFolder' => $PreviewThemeFolder));
      Redirect('/');
   }