Fix NPE in restoring network policies

When backing up network policies, we write null for policies that are
null or are inferred. When restoring, this sends null policies to be set
which results in a NPE.

Bug: 79961560
Test: 1) atest NetworkPolicyManagerServiceTest
2) Manual: adb restore using backup set with null policies does not
crash

Change-Id: I450685e38acae0658ea984b86ca8b17ca27a71a6

services/core/java/com/android/server/net/NetworkPolicyManagerService.java

@@ -2706,6 +2706,9 @@ public class NetworkPolicyManagerService extends INetworkPolicyManager.Stub {
     private void normalizePoliciesNL(NetworkPolicy[] policies) {
         mNetworkPolicy.clear();
         for (NetworkPolicy policy : policies) {
+            if (policy == null) {
+                continue;
+            }
             // When two normalized templates conflict, prefer the most
             // restrictive policy
             policy.template = NetworkTemplate.normalize(policy.template, mMergedSubscriberIds);

services/tests/servicestests/src/com/android/server/NetworkPolicyManagerServiceTest.java

@@ -1628,6 +1628,20 @@ public class NetworkPolicyManagerServiceTest {
         }
     }
 
+    /**
+     * Test that policy set of {null, NetworkPolicy, null} does not crash and restores the valid
+     * NetworkPolicy.
+     */
+    @Test
+    public void testSetNetworkPolicies_withNullPolicies_doesNotThrow() {
+        NetworkPolicy[] policies = new NetworkPolicy[3];
+        policies[1] = buildDefaultFakeMobilePolicy();
+        setNetworkPolicies(policies);
+
+        assertNetworkPolicyEquals(DEFAULT_CYCLE_DAY, mDefaultWarningBytes, mDefaultLimitBytes,
+                true);
+    }
+
     private SubscriptionPlan buildMonthlyDataPlan(ZonedDateTime start, long limitBytes) {
         return SubscriptionPlan.Builder
                 .createRecurringMonthly(start)