public ResponseCacheControl build() {
            return new ResponseCacheControl(maxAge, sharedMaxAge, mustRevalidate, noCache, noStore, cachePrivate, proxyRevalidate,
                    cachePublic, staleWhileRevalidate, staleIfError, noCacheFields, mustUnderstand, immutable);
        }
Returns the 'immutable' Cache-Control directive status.

@return true if the 'immutable' directive is present in the Cache-Control header.
httpclient5-cache/src/main/java/org/apache/hc/client5/http/cache/ResponseCacheControl.java