protected function _render($context = null)
    {
        if ($context === null) {
            throw $this->_createInvalidArgumentException(
                $this->__('Cannot render with a null context'),
                null,
                null,
                $context
            );
        }

        try {
            $expr = $this->_containerGet($context, ExprCtx::K_EXPRESSION);
            $result = $this->_renderExpression($expr, $context);

            return $result;
        } catch (NotFoundExceptionInterface $notFoundException) {
            throw $this->_createInvalidArgumentException(
                $this->__('Context does not contain an expression'),
                null,
                $notFoundException,
                $context
            );
        }
    }