empty elements in symfony form collection

I have a simple form with collection of items in it. Just like described here: http://symfony.com/doc/current/cookbook/form/form_collections.html.

The problem is when I add new element (or multiple elements) WITHOUT touching enything in them (not changing theirs inputs) I get an empty collection.

I would like to get a collection of added elements regardless theirs content. And even if there are fields are empty it would be ok.

In my case after form submission I have:

var_dump($request->get('my_form_name'));

/* dump result: 
array (size=19)
   ...
   'partners' => 
    array (size=1)
        0 => 
          array (size=2)
            'fullname' => string '' (length=2)
            'manager' => string '' (length=0)
   ...
*/

var_dump($form->getData()->getPartners()); 
// EMPTY!!! WTF? I expect an array of 1 element of Partner class which fields are set to '' and ''

On the other hand if somethig is set then it is ok:

var_dump($request->get('my_form_name'));

/* dump result: 
array (size=19)
   ...
   'partners' => 
    array (size=1)
        0 => 
          array (size=2)
            'fullname' => string ' NAME HERE ' (length=2)
            'manager' => string '' (length=0)
   ...
*/

var_dump($form->getData()->getPartners()); 
// ok, we have an array of 1 element which is an object of Partner class

Any ideas how to get rid of that bug?

---

UPDATED

Partner’s class mapping is:

BundleEntityPartner:
  ...
  fields:
    fullname: 
      type: string
      lenght: 255
      nullable: True
    manager: 
      type: string
      lenght: 255
      nullable: True
  manyToOne:
    owner:
      targetEntity: Step2
      inversedBy: partners
      joinColumn:
        name: owner_id
        referencedColumnName: id

field partners is added to the form of Step2 entity like collection with allow_add, allow_delete, by_reference set to false

Answer

ok, I found a problem.

I must to set empty_data in subform (Partner class).

---

I don’t understand why but when all fields of related class (Partners) are submitted to be "" (empty) then in method sumbit of class SymfonyComponentFormForm the block

            if (FormUtil::isEmpty($viewData)) {
                $emptyData = $this->config->getEmptyData();

                if ($emptyData instanceof Closure) {
                    /* @var Closure $emptyData */
                    $emptyData = $emptyData($this, $viewData);
                }

                $viewData = $emptyData;
            }

gives null in $viewData for Partner of empty fields. For object submitted to be the Partner with at least one field not empty $viewData is needed object.

---

All that is because

$this->config->getEmptyData() 

for empty object is Closure which eventually results to null, but for Partner with at least one field not empty it gives directly needed object.