php - Uncaught Error in try catch block

I am trying to write "universal" function to execute SQL query and return JSON and handle error within. And during process there is something I don't understand - why try catch block doesn't handle error. (Later I will improve logic - question is NOT about that, but purely about error handling).

Here is my code:

public
function sqlToJSON($query, $type = array(), $params = array())
{
    try {
        $data = array();
        $stmt = $this->mysqli->prepare($query);
        if (count($type) > 0 && count($params) > 0) {
            call_user_func_array(array($stmt, "bind_param"), array_merge(array($type), $params));
        }

        $stmt->execute();
        $result = $stmt->get_result();
        while ($row = $result->fetch_assoc()) {
            $data[] = $row;
        }
        $stmt->free_result();
        $stmt->close();
        return array('result' => 'success', 'error' => null, 'data' => $data);
    } catch (Exception $e) {
        $this->sqlError = 'Caught exception: ' . $e->getMessage();

        return array('result' => 'failed', 'error' => $e->getMessage(), 'data' => null);
    }
}

How I call this function:

    $q = 'INSERT INTO receivers (receiver_name, owner) VALUES (UPPER(?), ?)';
    $params = array(&$receiverName, &$clientEmail);
    $this->sqlToJSON($q, 'ss', $params);

This gives following expected error:

Uncaught Error: Call to a member function fetch_assoc() on boolean in ...

What I don't understand why catch block is not executed in this case?

Answer

In php errors are not exceptions. If you want to catch them, write your own error_handler. http://php.net/manual/en/function.set-error-handler.php