public static String maybeRootCauseReason(JsonNode root) {
    // Prefer the root cause to an arbitrary reason.
    String message;
    if (!root.findPath("root_cause").isMissingNode()) {
      message = root.findPath("root_cause").findPath("reason").textValue();
    } else {
      message = root.findPath("reason").textValue();
    }
    return message;
  }
Returns the {@linkplain HttpHeaders headers} for this request.
zipkin-storage/elasticsearch/src/main/java/zipkin2/elasticsearch/internal/client/HttpCall.java