Only notify of new link properties if they are non-null

Bug: 21147252
Change-Id: I5552a167425b0d54b22003a3675b560ee0b0da19
diff --git a/service/java/com/android/server/wifi/WifiStateMachine.java b/service/java/com/android/server/wifi/WifiStateMachine.java
index a65e14a..1b6b46a 100644
--- a/service/java/com/android/server/wifi/WifiStateMachine.java
+++ b/service/java/com/android/server/wifi/WifiStateMachine.java
@@ -4100,7 +4100,11 @@
                         + " old: " + mLinkProperties + " new: " + newLp);
             }
             mLinkProperties = newLp;
-            mIpReachabilityMonitor.updateLinkProperties(mLinkProperties);
+            if (mLinkProperties != null) {
+                mIpReachabilityMonitor.updateLinkProperties(mLinkProperties);
+            } else {
+                mIpReachabilityMonitor.clearLinkProperties();
+            }
             if (mNetworkAgent != null) mNetworkAgent.sendLinkProperties(mLinkProperties);
         }