Fixed NPE when wifi is turned off.

Change-Id: If1f12cdd60677c4779fa5427a0a1a80d712149d5
diff --git a/services/core/java/com/android/server/net/NetworkPolicyManagerShellCommand.java b/services/core/java/com/android/server/net/NetworkPolicyManagerShellCommand.java
index a626b5b..9cfb590 100644
--- a/services/core/java/com/android/server/net/NetworkPolicyManagerShellCommand.java
+++ b/services/core/java/com/android/server/net/NetworkPolicyManagerShellCommand.java
@@ -24,6 +24,7 @@
 
 import java.io.PrintWriter;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
@@ -364,9 +365,12 @@
     private List<NetworkPolicy> getWifiPolicies() throws RemoteException {
         // First gets a list of saved wi-fi networks.
         final List<WifiConfiguration> configs = mWifiManager.getConfiguredNetworks();
-        final Set<String> ssids = new HashSet<>(configs.size());
-        for (WifiConfiguration config : configs) {
-            ssids.add(removeDoubleQuotes(config.SSID));
+        final int size = configs != null ? configs.size() : 0;
+        final Set<String> ssids = new HashSet<>(size);
+        if (configs != null) {
+            for (WifiConfiguration config : configs) {
+                ssids.add(removeDoubleQuotes(config.SSID));
+            }
         }
 
         // Then gets the saved policies.