code: public function getDefault(Message $message = null)
      {
          if (null === $this->default) {
              if ($this->useTypeDefault) {
                  return $this->isASingleValue() ? $this->type->getDefault() : [];
              }
              return $this->isASingleValue() ? null : [];
          }
  
          if ($this->default instanceof \Closure) {
              $default = call_user_func($this->default, $message, $this);
              $this->guardDefault($default);
              if (null === $default) {
                  if ($this->useTypeDefault) {
                      return $this->isASingleValue() ? $this->type->getDefault() : [];
                  }
                  return $this->isASingleValue() ? null : [];
              }
              return $default;
          }
  
          return $this->default;
      }
docs: @param Message $message
  
  @return mixed