MySQLi returns empty query, why?

Question

PHP

Hello.
Help, I don't understand the problem at all.
Created a mini module, the model sends a SELECT request to receive goods.
In response , nothing , just an empty array, although the request is completely correct. Through phpMyAdmin without errors.
I tried to correct and so on, information related to the oc_product * tables is not displayed at all. Brings out with others.
Request:

SELECT p.`product_id` FROM `oc_product` p LEFT JOIN `oc_product_description` pd ON (p.`product_id` = pd.`product_id`) WHERE pd.`language_id` = '3' AND p.`status` = '1' AND p.`date_available` <= NOW() AND pd.`name` LIKE '%дрова%' ORDER BY p.product_id DESC LIMIT 50

I use MySQLi, OpenCart 2.0, PHP 5.6.
Help me please.
ps Missing code
$query = $this->db->query($sql);
In $this->db:

public function query($sql) {
    $query = $this->connection->query($sql);

    if (!$this->connection->errno) {
      if ($query instanceof \mysqli_result) {
        $data = array();

        while ($row = $query->fetch_assoc()) {
          $data[] = $row;
        }

        $result = new \stdClass();
        $result->num_rows = $query->num_rows;
        $result->row = isset($data[0]) ? $data[0] : array();
        $result->rows = $data;

        $query->close();

        return $result;
      } else {
        return true;
      }
    } else {
      throw new \Exception('Error: ' . $this->connection->error  . '<br />Error No: ' . $this->connection->errno . '<br />' . $sql);
    }
  }