code: final public function populateDefaults($fieldName = null)
      {
          $this->guardFrozenMessage();
  
          if (!empty($fieldName)) {
              $this->populateDefault(static::schema()->getField($fieldName));
              return $this;
          }
  
          foreach (static::schema()->getFields() as $field) {
              $this->populateDefault($field);
          }
  
          return $this;
      }
docs: {@inheritdoc}
  @return static