Steps to reproduce:

1. Create new form type class like:

   class HistorySliderType extends AbstractType
   {
       /**
        * {@inheritdoc}
        */
       public function buildForm(FormBuilder $builder, array $options)
       {
           $datetime = new \DateTime();
   
           $builder
               ->add('date', 'datetime', array(
                   'date_widget' => 'single_text',
                   'time_widget' => 'single_text',
                   'date_format' => 'yyyy-MM-dd',
                   'with_seconds' => true,
                   'data' => $datetime
               ));
       }
   
       /**
        * {@inheritdoc}
        */
       function getName()
       {
           return 'acme_tbundle_historyslidertype';
       }
   }
   

2. Render the form

The result: Expected argument of type "DateTime", "array" given