code: public void transfer(Integer namespaceId, Integer projectId) throws IOException {
          Query query = new Query().append("namespace", String.valueOf(namespaceId));
          String tailUrl = GitlabProject.URL + "/" + projectId + "/transfer" + query.toString();
          retrieve().method(PUT).to(tailUrl, Void.class);
      }
docs: Transfer a project to the given namespace
  
  @param namespaceId Namespace ID
  @param projectId   Project ID
  @throws IOException on gitlab api call error