public long maxStaleSeconds() {
        return maxStaleSeconds < 0 ? -1 : maxStaleSeconds;
    }
Returns the value of the {@code "max-stale"} directive or {@code -1} if disabled or the value is not
specified.

@see #hasMaxStale()
core/src/main/java/com/linecorp/armeria/common/ClientCacheControl.java