Call to a member function on a non-object error symfony2 - forms

Question

This is an odd one. I have this method, that is the callback for the FormEvents::POST_SET_DATA event in an EventSubscriber of a form in Symfony2:
public function preSetData(FormEvent $event)
{
$data = $event->getData();
$form = $event->getForm();
$resource_provider = $data->getResourceProvider();
$type = $resource_provider->getType(); //PROBLEM HERE
\Doctrine\Common\Util\Debug::dump(is_object($resource_provider));
}
It has more code but the error is firing in the line with the comment PROBLEM HERE.
The issue is that the dump there prints bool(true), so it is an object, and have the data inside, but trying to call getType(), that exist, fails with this error:
Error: Call to a member function getType() on a non-object
To add more confusion, if I dump $resource_provider->getType() I get the expected content dumped, but the error remains.
Does someone knows or has a clue on what can be happening here?
EDIT
Can't believe it! I found the answer, but doesn't makes sense at all! I had to wrap the problematic code with a conditional like this:
if(is_a($resource_provider, 'My\Bundle\Path\Entity\ResourceProvider')){}
and it worked! If someone can tell me what is the sense of that, I will happily select his/her answer as correct.

Answer 1

The problem is that $resource_provider is probably null as error says $resource_provider is not an object.
When printing the value of $resource_provider and skipping the script, it shows the right object of class 'My\Bundle\Path\Entity\ResourceProvider' :
echo get_class($resource_provider); exit; // Display My\Bundle\Path\Entity\ResourceProvider and skip the script
When adding a condition to test is the object is of the expected class, the script doesn't crash anymore :
if(is_a($resource_provider, 'My\Bundle\Path\Entity\ResourceProvider')){}
In addition, when skipping script when it's not an object, $resource_provider is null and the script skipped :
if(is_a($resource_provider, 'My\Bundle\Path\Entity\ResourceProvider')){
} else {
var_dump($resource_provider); exit;
}
$resource_provider is an object and null in the same "execution" of the script.
So we can deduce that the EventSubcriber is loaded more than one time, perhaps before the form binding and after form binding for example and the first time with the expected object, and a second (or more) time with no value, as null, perhaps because the $resource_provider is not filled when submitting form or something else.