public LogWriterBuilder failureResponseLogLevel(LogLevel failedResponseLogLevel) {
        requireNonNull(failedResponseLogLevel, "failedResponseLogLevel");
        return responseLogLevelMapper(log -> log.responseCause() != null ? failedResponseLogLevel : null);
    }
Sets the {@link LogLevel} to use when logging failure responses (e.g., failed with an exception).
{@link LogLevel#WARN} will be used by default.
core/src/main/java/com/linecorp/armeria/common/logging/LogWriterBuilder.java