Act on a newly created entity.
This hook runs after a new entity object has just been instantiated. It can be used to set initial values, e.g. to provide defaults.
\Drupal\Core\Entity\EntityInterface $entity: The entity object.
Note: this list is generated by pattern matching, so it may include some functions that are not actually implementations of this hook.
function hook_entity_create(\Drupal\Core\Entity\EntityInterface $entity) {
  // @todo Remove the check for EntityNG once all entity types have been
  //   converted to it.
  if (!isset($entity->foo) && $entity instanceof \Drupal\Core\Entity\EntityNG) {
    $entity->foo->value = 'some_initial_value';
  }
}