private void validateUdsArguments() {
        if (this.secure) {
            throw new UnsupportedOperationException("HTTPS is not supported over a UDS connection");
        } else if (this.localAddress != null) {
            throw new UnsupportedOperationException("A localAddress cannot be specified for a UDS connection");
        } else if (this.proxyChain != null) {
            throw new UnsupportedOperationException("Proxies are not supported over a UDS connection");
        } else if (this.layered != LayerType.PLAIN) {
            throw new UnsupportedOperationException("Layering is not supported over a UDS connection");
        } else if (this.tunnelled != TunnelType.PLAIN) {
            throw new UnsupportedOperationException("Tunnelling is not supported over a UDS connection");
        }
    }
Whether the route is (supposed to be) secure.
httpclient5/src/main/java/org/apache/hc/client5/http/HttpRoute.java