code: public static SematextClient newInstance(String token, ExecutorService executor) {
      if (token == null) {
        throw new IllegalArgumentException("Token should be defined.");
      }
      if (executor == null) {
        throw new IllegalArgumentException("Executor should be defined.");
      }
      return new SematextClient(new ClientProperties(token, null, executor));
    }
docs: Create new instance of client.
  @param token token
  @param executor executor
  @return new client instance
  @throws IllegalArgumentException when token or executor is {@code null}