phpunit InvalidArgumentException: The current node list is empty - symfony

Question

Running a test which has this line:
$authorizeForm = $crawler->selectButton('Authorize')->form();
outputs this error:
There was 1 error:
1) Citiqa\ApiBundle\Tests\Controller\SecurityControllerTest::testLoginAndAuthorize
InvalidArgumentException: The current node list is empty.
/home/oris/src/citiqa-api/vendor/symfony/symfony/src/Symfony/Component/DomCrawler/Crawler.php:648
/home/oris/src/citiqa-api/src/Citiqa/ApiBundle/Tests/Controller/SecurityControllerTest.php:28
I've taken a look at Crawler.php and saw the problematic function:
public function form(array $values = null, $method = null)
{
//var_dump($this);
if (!count($this)) {
throw new \InvalidArgumentException('The current node list is empty.');
}
$form = new Form($this->getNode(0), $this->uri, $method);
if (null !== $values) {
$form->setValues($values);
}
return $form;
}
$this is in this case the crawler object which extends \SplObjectStorage which implements the Countable interface, so we should be fine. I've tried to var_dump($this); on form() and I see this:
object(Symfony\Component\DomCrawler\Crawler)#1354 (2) {
["uri":"Symfony\Component\DomCrawler\Crawler":private]=>
string(37) "https://localhost/oauth/v2/auth_login"
["storage":"SplObjectStorage":private]=>
array(1) {
["0000000075b694bd000000002b32afe0"]=>
array(2) {
["obj"]=>
object(DOMElement)#529 (18) {
["tagName"]=>
string(6) "button"
["schemaTypeInfo"]=>
NULL
["nodeName"]=>
string(6) "button"
["nodeValue"]=>
string(5) "login"
["nodeType"]=>
int(1)
["parentNode"]=>
string(22) "(object value omitted)"
["childNodes"]=>
string(22) "(object value omitted)"
["firstChild"]=>
string(22) "(object value omitted)"
["lastChild"]=>
string(22) "(object value omitted)"
["previousSibling"]=>
string(22) "(object value omitted)"
["nextSibling"]=>
string(22) "(object value omitted)"
["attributes"]=>
string(22) "(object value omitted)"
["ownerDocument"]=>
string(22) "(object value omitted)"
["namespaceURI"]=>
NULL
["prefix"]=>
string(0) ""
["localName"]=>
string(6) "button"
["baseURI"]=>
NULL
["textContent"]=>
string(5) "login"
}
["inf"]=>
NULL
}
}
}
object(Symfony\Component\DomCrawler\Crawler)#1852 (2) {
["uri":"Symfony\Component\DomCrawler\Crawler":private]=>
string(155) "https://localhost/oauth/v2/auth?client_id=1_5ndcb2XXXXX&redirect_uri=http%3A%2F%2Fwww.google.com&response_type=token"
["storage":"SplObjectStorage":private]=>
array(0) {
}
}
phpunit version is 3.6.10
Funny thing is, this test is completing successfully on another machine, with a different phpunit version (3.7.21). could this be a version / error reporting level issue?