code: private function getEscapedValues(): array
      {
          $parameters = [];
  
          foreach ($this->parameters['parameters'] as $key => $value) {
              if (\is_string($value)) {
                  if (0 === strncmp($value, '@', 1)) {
                      $value = '@'.$value;
                  }
  
                  if (false !== strpos($value, '%')) {
                      $value = str_replace('%', '%%', $value);
                  }
              }
  
              $parameters[$key] = $value;
          }
  
          return ['parameters' => $parameters];
      }
docs: Escapes % and @.
  
  @return array<string,string[]>
  
  @see http://symfony.com/doc/current/service_container/parameters.html#parameters-in-configuration-files