Extend function doesn't work

[ConstantineYurevich]

Code of extend function:

    public function extend($ttl = null)
    {
        if ($this->isDisabled()) {
            return false;
        }
        return $this->set($this->get(), $ttl);
    }

While set function doesn't have $ttl attribute:

   public function set($value)
    {
        if (!isset($this->key)) {
            return false;
        }

        if ($this->isDisabled()) {
            return $this;
        }

        $this->data = $value;
        return $this;
    }