Symfony form submission with handleRequest issue - symfony

Question

I'm experiencing an odd error with my form validation in Symfony 4. It is a simple contact form represented by this entity:
class ContactRequest
{
/** #var int */
private $id;
/** #var string */
private $fullName;
//...
/**
* #return string
*/
public function getFullName() : string
{
return $this->fullName;
}
In my controller I'm handling the submission as per Symfony website but there is something I'm missing for I'm getting the following error:
Type error: Return value of App\Entity\ContactRequest::getFullName() must be of the type string, null returned
Now, I know what is the meaning of that: it expects a string to be returned by the method getFullName whereas null is actually returned but I don't understand why.
This is my controller
public function contactSubmit(Request $request, ValidatorInterface $validator)
{
$form = $this->createForm(ContactType::class);
$form->handleRequest($request);
if($form->isValid()){
//...
}
$errors = $validator->validate($form);
Shouldn't the handleRequest() method set the values in the entity for me?
To my surprise, when I have initialised the entity before, it worked well notwithstanding the entity is already set in the configureOptions() method in the form:
$contact = new ContactRequest;
$contact
->setFullName($request->request->get('contact')['fullName'])
//...
$form = $this->createForm(
ContactType::class
$contact
);
$form->setData($contact);
$form->handleRequest($request);
However, shouldn't the scope of using the handleRequest() be to avoid setting the entity's values manually? Shouldn't the handleRequest() method take care of setting those values?
I know I could validate the submitted data against the entity too (thing that I've successfully tried), without using the handleRequest() at all but it would piss me off a little. Why would I need to set a form in such a case?
This is the ContactType form:
//...
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('fullName', TextType::class, [
'required' => true,
'empty_data' => 'a',
'attr' => [
'placeholder' => 'Full Name',
'class' => 'form-control'
]
])
//...
}
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults([
'data_class' => ContactRequest::class
]);
}

Answer 1

In order to find out where your getFullName gets called you could (atleast in dev environment) print the backtrace on the call:
/**
* #return string
*/
public function getFullName() : string
{
if ($this->fullName === null)
{
echo "<pre>getFullName on uninitialized entity:\n";
debug_print_backtrace();
die();
}
return $this->fullName;
}
But as said in the comments: Initializing the entity with a null value in that field and not allowing the getter to return a null value seems kinda odd to me, so : ?string to allow for nullable return values (as of PHP 7.1) seems to be the next best option.