Behat Mink: getAttribute returns WebDriver\Execute Object instead of value

I use Appium+Selenium2+Behat+Mink, when I try to get attribute by the following code:

$id = $this->getSession()->getPage()->find('xpath', $xpath)->getAttribute("id");

I get something like this:

WebDriver\Execute Object
        (
            [url:protected] => 0.0.0.0:4723/wd/hub/session/b1892305-af0b-4bf3-a197-3f58d5ef6954/execute
        )