presto-elasticsearch/src/main/java/io/prestosql/elasticsearch/client/NodesResponse.java/Node/Node
class Node:        @JsonCreator
        public Node(
                @JsonProperty("roles") Set<String> roles,
                @JsonProperty("http") Optional<Http> http)
        {
            this.roles = ImmutableSet.copyOf(roles);
            this.http = requireNonNull(http, "http is null");
        }