* @return A Promise that will be resolved with the response or rejected with an error.
     */
    public Deferred<T>.Promise execute(final Client client) {
        final String error = getValidationError();
        if (!Strings.isNullOrEmpty(error)) {
            throw new IllegalArgumentException(error);
        }

        final Deferred<T> deferred = new Deferred<>();
        try {

            @Override
            public void onFailure(final Exception e) {
                deferred.reject(e);
            }
        });
    }

    @Override
    protected String getValidationError() {
        return null;
    }

    /**
     * Builds the OpenSearch query for popular words.
     * @return The QueryBuilder instance.
     */
    protected QueryBuilder buildQuery() {