public function create($customerId, $parameters = [])
    {
        if (is_array($parameters) && isset($parameters['source'])) {
            $parameters['source']['object'] = 'bank_account';
        } elseif (is_string($parameters)) {
            $parameters = ['source' => $parameters];
        }

        return $this->_post("customers/{$customerId}/sources", $parameters);
    }