You could remove some duplication with a getPortraitValue function:

function getPortraitValue($apiData, $key) {
    $value = $apiData['portrait'][$key];
    if (isset($value)) {
        return $value;
    }
    return null;
}

$portrait = new Portrait();
$portrait->setXCoordinate(getPortraitValue($apiData, 'x')
    ->setYCoordinate(getPortraitValue($apiData, 'y'))
    ->setWidth(getPortraitValue($apiData, 'w'))
    ->setHeight(getPortraitValue($apiData, 'h'))
    ->setOffset(getPortraitValue($apiData, 'offset')
    ->setUrl(getPortraitValue($apiData, 'url');
return $portrait;

You could remove some duplication with a getPortraitValue function:

function getPortraitValue($apiData, $key) {
    $portrait = $apiData['portrait'];
    if (isset($portrait[$key])) {
        return $portrait[$key];
    }
    return null;
}

$portrait = new Portrait();
$portrait->setXCoordinate(getPortraitValue($apiData, 'x')
    ->setYCoordinate(getPortraitValue($apiData, 'y'))
    ->setWidth(getPortraitValue($apiData, 'w'))
    ->setHeight(getPortraitValue($apiData, 'h'))
    ->setOffset(getPortraitValue($apiData, 'offset')
    ->setUrl(getPortraitValue($apiData, 'url');
return $portrait;