public function buildForm(FormBuilder $builder, array $options) {
        $builder->add('start', 'datetime', array('date_widget' => 'single_text', 'time_widget' => 'single_text'));
        $builder->add('end', 'datetime', array('date_widget' => 'single_text', 'time_widget' => 'single_text'));
        $builder->add('journeytime');
        $builder->add('content');
        if (count($this->secondaryCategories) > 0) {
            $builder->add('secondaryCategory', 'entity', array('class' => 'ACMEContactBundle:SecondaryCategory', 'empty_value' => 'Bitte auswählen...'));
        }
        $builder->add('initiator', 'entity', array('class' => ACME\\MasterdataBundle\\Entity\\PartyInstance',
            'query_builder' => $this->qb
        ));
    }

public function getDefaultOptions(array $options) {
        $collectionConstraint = new Collection(array(
                    'secondaryCategory' => new Assert\NotBlank()
                ));

        if (count($this->secondaryCategories) > 0) {
            return array(
                'data_class' => 'ACME\ContactBundle\Entity\Visit',
                'validation_constraint' => $collectionConstraint,
            );
        }

        return array(
            'data_class' => 'ACME\ContactBundle\Entity\Visit',
        );
    }

Expected argument of type array or Traversable and ArrayAccess, object given