Bug fix

https://github.com/2dust/v2rayNG/issues/5151

V2rayNG/app/src/main/java/com/v2ray/ang/fmt/Hysteria2Fmt.kt

@@ -101,7 +101,7 @@ object Hysteria2Fmt : FmtBase() {
             Hysteria2Bean.TransportBean(
                 type = "udp",
                 udp = Hysteria2Bean.TransportBean.TransportUdpBean(
-                    hopInterval = (config.portHoppingInterval ?: "30") + "s"
+                    hopInterval = (config.portHoppingInterval?.takeIf { it.isNotEmpty() } ?: "30") + "s"
                 )
             )