public boolean isStaleIfErrorEnabled() {
        return this.staleIfErrorEnabled;
    }
Returns a boolean value indicating whether the stale-if-error cache
directive is enabled. If this option is enabled, cached responses that
have become stale due to an error (such as a server error or a network
failure) will be returned instead of generating a new request. This can
help to reduce the load on the origin server and improve performance.
@return {@code true} if the stale-if-error directive is enabled, or
{@code false} otherwise.
httpclient5-cache/src/main/java/org/apache/hc/client5/http/impl/cache/CacheConfig.java