logger.warn("Failed to access Web API.", e);
                message = e.getMessage();
            } else {
                final String errorCode = UUID.randomUUID().toString();
                message = "[" + errorCode + "] Failed to access to Web API.";
                logger.warn(message, e);
            }
            response.sendError(e.getStatusCode(), message);
        }
    }

        } else {
            final String errorCode = UUID.randomUUID().toString();
            message = escapeJsonKeyValue("error_code:", errorCode);
            if (logger.isDebugEnabled()) {
                logger.debug("[{}] {}", errorCode, stacktraceString.get().replace("\n", "\\n"));
            } else {
                logger.warn("[{}] {}", errorCode, t.getMessage());
            }
        }

        } catch (final S3Exception e) {
            logger.warn("Failed to access object with error code {}: bucket={}, path={}", e.awsErrorDetails().errorCode(), bucketName, path,
                    e);
        } catch (final Exception e) {
            logger.warn("Failed to get object head: bucket={}, path={}", bucketName, path, e);
        }
        return null;
    }