static function isSupportedTheme($theme)
	{
		if (! is_string($theme) || empty($theme)) {
			throw new InvalidCallException('Invalid theme value : empty or null value');
		}
		return file_exists(Yii::getAlias(BootswatchAsset::VENDOR_ALIAS . '/' . strtolower($theme) . '/bootstrap.min.css'));
	}