Symfony get query from form with some empty text areas

I'd like to know if there is anyway to get a query result from the text areas that have been filled while some have not.

Example:

$form = $this->get('form.factory')->create(new UsersType(), new Users())
            ->add('firstname', 'text', array('required' => false, 'label' => 'First name '))
            ->add('lastname', 'text', array('required' => false, 'label' => 'Last name '))
        ;

$idm = $em->getRepository('MyBundle:Users')->findBy(
                array('number' => $form->get('number')->getData(),
                    'firstname' => $form->get('firstname')->getData(),
                    'lastname' => $form->get('lastname')->getData()
            ));

I would like that it ignores the texts which have not been filled and execute a query only with the filled texts.

Thank you!