ContentEntityForm::copyFormValuesToEntity

protected ContentEntityForm::copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state)

protected function copyFormValuesToEntity(EntityInterface $entity, array $form, FormStateInterface $form_state) {
  // First, extract values from widgets.
  $extracted = $this->getFormDisplay($form_state)->extractFormValues($entity, $form, $form_state);

  // Then extract the values of fields that are not rendered through widgets,
  // by simply copying from top-level form values. This leaves the fields
  // that are not being edited within this form untouched.
  foreach ($form_state->getValues() as $name => $values) {
    if ($entity->hasField($name) && !isset($extracted[$name])) {
      $entity->set($name, $values);
    }
  }
}