diff -r 43eee1237934 -r 6f12009ea9d7 src/java.base/share/classes/java/net/MulticastSocket.java
--- a/src/java.base/share/classes/java/net/MulticastSocket.java	Thu Nov 28 18:30:18 2019 +0100
+++ b/src/java.base/share/classes/java/net/MulticastSocket.java	Thu Nov 28 16:49:52 2019 +0000
@@ -576,7 +576,7 @@
     public NetworkInterface getNetworkInterface() throws SocketException {
         NetworkInterface ni
             = (NetworkInterface)getImpl().getOption(SocketOptions.IP_MULTICAST_IF2);
-        if ((ni.getIndex() == 0) || (ni.getIndex() == -1)) {
+        if (ni == null) {
             InetAddress[] addrs = new InetAddress[1];
             addrs[0] = InetAddress.anyLocalAddress();
             return new NetworkInterface(addrs[0].getHostName(), 0, addrs);