docs: public String queryPlan( String query,
                               String queryLanguage ) {
          String url = jsonRestClient.appendToURL(QUERY_PLAN_METHOD);
          String contentType = contentTypeForQueryLanguage(queryLanguage);
          JSONRestClient.Response response = jsonRestClient.postStreamTextPlain(new ByteArrayInputStream(query.getBytes()), url,
                                                                                contentType);
          if (!response.isOK()) {
              throw new RuntimeException(JdbcI18n.invalidServerResponse.text(url, response.asString()));
          }
          return response.asString();
      }