static Duration validateNonNegative(Duration duration, String fieldName) {
        if (duration.isNegative()) {
            throw new IllegalArgumentException(fieldName + ": " + duration + " (expected: >= 0)");
        }
        return duration;
    }
Initialized later by {@link Server} via {@link #setServer(Server)}.
core/src/main/java/com/linecorp/armeria/server/DefaultServerConfig.java