Error when there are no results for availableNumbers

[braxter]

When searching for availableNumbers, the response for an empty result is as follows:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<SearchResult/>

The PHP code when requesting availableNumbers attempts to access 'ResultCount' causing an error(Notice).

    public function availableNumbers($filters=Array()){
        //...
        $url = sprintf('%s/%s', $this->account_id, 'availableNumbers');
        $data = parent::_get($url, $filters);
        $count = $data['ResultCount'];