docs: public boolean aliasExists(String alias) {
          try {
              final JestResult result = jestClient.execute(new GetSettings.Builder().addIndex(alias).build());
              return result.isSucceeded() && !Iterators.contains(result.getJsonObject().fieldNames(), alias);
          } catch (IOException e) {
              throw new ElasticsearchException("Couldn't check existence of alias " + alias, e);
          }
      }