Spring boot with elastic fail while index exists

I'm trying to connect a Spring boot application with ElasticSearch, but I get the next error:

Constructor threw exception; nested exception is org.springframework.data.elasticsearch.ElasticsearchException: Error while for indexExists request: org.elasticsearch.action.admin.indices.get.GetIndexRequest

Configuration class

@Configuration
@EnableElasticsearchRepositories(basePackages = "com.repository")
public class ESConfig extends AbstractElasticsearchConfiguration {

    @Override
    @Bean
    public RestHighLevelClient elasticsearchClient() {

        final ClientConfiguration clientConfiguration = ClientConfiguration.builder()  
            .connectedTo("ElasticSearch Server")
            .withBasicAuth("user", "password").build();

        return RestClients.create(clientConfiguration).rest();                         
    }

}

Entity :

@Document(indexName = "flight")
public class FlightPositionES {

    @Id
    private Long id;
    private String ident;
    private String airGround;
    private Double altitude;
    private Integer clock;
    private String flightId;
    private Double groundSpeed;
    private Double heading;
    private GeoPoint location;
    private String aircraftRegistration;
}

Repository:

public interface IFlightPositionESRepository extends ElasticsearchCrudRepository<FlightPositionES, Long> {

}