eZ\Publish\Core\REST\Server\Controller\Content::publishVersion PHP Method

    public function publishVersion($contentId, $versionNumber)
    {
        $versionInfo = $this->repository->getContentService()->loadVersionInfo($this->repository->getContentService()->loadContentInfo($contentId), $versionNumber);
        if ($versionInfo->status !== VersionInfo::STATUS_DRAFT) {
            throw new ForbiddenException('Only version in status DRAFT can be published');
        }
        $this->repository->getContentService()->publishVersion($versionInfo);
        return new Values\NoContent();
    }

 /**
  * If the published content is a user, return directly without publishing.
  *
  * @param mixed $contentId
  * @param int $versionNumber
  *
  * @return \eZ\Publish\Core\REST\Server\Values\NoContent
  */
 public function publishVersion($contentId, $versionNumber)
 {
     if (!$this->isUserContent($contentId)) {
         parent::publishVersion($contentId, $versionNumber);
     }
     return new NoContent();
 }