Fix NPE in ConnectivityService

bug:11727708
Change-Id: Ia8ca9d1e23f021feaf4b772ec38d1d0e89b0cd2a
diff --git a/services/java/com/android/server/ConnectivityService.java b/services/java/com/android/server/ConnectivityService.java
index 478f8c7..baff661 100644
--- a/services/java/com/android/server/ConnectivityService.java
+++ b/services/java/com/android/server/ConnectivityService.java
@@ -3457,7 +3457,7 @@
         synchronized (mProxyLock) {
             if (mDefaultProxy != null && mDefaultProxy.equals(proxy)) return;
             if (mDefaultProxy == proxy) return; // catches repeated nulls
-            if (!proxy.isValid()) {
+            if (proxy != null &&  !proxy.isValid()) {
                 if (DBG) log("Invalid proxy properties, ignoring: " + proxy.toString());
                 return;
             }