Issue #3047864 by joseph.olstad, Anatoliy Vorobyov: Blank pages for admin

    $this->deprecated = [];

    foreach ($deprecated as $deprecatedName => $deprecatedSetting) {

      if (!is_null($deprecatedSetting)) {

        $key = $deprecatedSetting->getDeprecatedReplacementSetting()->getPluginId();

        if (!isset($this->deprecated[$key])) {

          $this->deprecated[$key] = [];

        }

        $this->deprecated[$key][$deprecatedName] = $deprecatedSetting;

      }

    }

    // Retrieve cache.

    $cache = $theme->getCache('settings');