Undefined index: day when there are no values yet

Notice: Undefined index: day in Drupal\office_hours\Plugin\Field\FieldWidget\OfficeHoursWidget->formElement() (line 143 of profiles/hungry_kickstart/modules/contrib/office_hours/src/Plugin/Field/FieldWidget/OfficeHoursWidget.php).
Drupal\office_hours\Plugin\Field\FieldWidget\OfficeHoursWidget->formElement(Object, 0, Array, Array, Object)
Drupal\Core\Field\WidgetBase->formSingleElement(Object, 0, Array, Array, Object)
Drupal\Core\Field\WidgetBase->formMultipleElements(Object, Array, Object)
Drupal\Core\Field\WidgetBase->form(Object, Array, Object)
Drupal\Core\Entity\Entity\EntityFormDisplay->buildForm(Object, Array, Object)
Drupal\Core\Entity\ContentEntityForm->form(Array, Object)
Drupal\node\NodeForm->form(Array, Object)
Drupal\Core\Entity\EntityForm->buildForm(Array, Object)
call_user_func_array(Array, Array)
Drupal\Core\Form\FormBuilder->retrieveForm('node_shop_form', Object)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object)
Drupal\Core\Entity\EntityFormBuilder->getForm(Object)
Drupal\node\Controller\NodeController->add(Object)
call_user_func_array(Array, Array)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\PageCache->pass(Object, 1, 1)
Drupal\Core\StackMiddleware\PageCache->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1)
Stack\StackedHttpKernel->handle(Object, 1, 1)
Drupal\Core\DrupalKernel->handle(Object)