[KV] Only discard state if non-null

To avoid NPEs. Added tests. This design is not optimal but left any
re-design to be done when we move applyStateTransition() to more upper
levels, which is going to happen when we extract package-backup.

Bug: 117269444
Test: atest FrameworksServicesRoboTests
Test: 1. Set BackupApp to time-out on agent onCreate()
      2. adb shell bmgr backupnow --non-incremental
         com.google.android.apps.backupapp
      3. Verify it doesn't crash
Change-Id: I7a3fd3d3d5a4b5931206564c197edd86b6321933
diff --git a/services/backup/java/com/android/server/backup/keyvalue/KeyValueBackupTask.java b/services/backup/java/com/android/server/backup/keyvalue/KeyValueBackupTask.java
index 6904b3f..3a5232a 100644
--- a/services/backup/java/com/android/server/backup/keyvalue/KeyValueBackupTask.java
+++ b/services/backup/java/com/android/server/backup/keyvalue/KeyValueBackupTask.java
@@ -708,8 +708,6 @@
             } else {
                 throw TaskException.create();
             }
-        } finally {
-            mBlankStateFile.delete();
         }
         checkAgentResult(packageInfo, agentResult);
     }
@@ -1037,8 +1035,13 @@
 
     private void cleanUpAgent(@StateTransaction int stateTransaction) {
         applyStateTransaction(stateTransaction);
-        mBackupDataFile.delete();
+        if (mBackupDataFile != null) {
+            mBackupDataFile.delete();
+        }
         mBlankStateFile.delete();
+        mSavedStateFile = null;
+        mBackupDataFile = null;
+        mNewStateFile = null;
         tryCloseFileDescriptor(mSavedState, "old state");
         tryCloseFileDescriptor(mBackupData, "backup data");
         tryCloseFileDescriptor(mNewState, "new state");
@@ -1059,7 +1062,9 @@
                 mNewStateFile.renameTo(mSavedStateFile);
                 break;
             case StateTransaction.DISCARD_NEW:
-                mNewStateFile.delete();
+                if (mNewStateFile != null) {
+                    mNewStateFile.delete();
+                }
                 break;
             case StateTransaction.DISCARD_ALL:
                 mSavedStateFile.delete();
diff --git a/services/robotests/src/com/android/server/backup/keyvalue/KeyValueBackupTaskTest.java b/services/robotests/src/com/android/server/backup/keyvalue/KeyValueBackupTaskTest.java
index fb57d68..7a847f3 100644
--- a/services/robotests/src/com/android/server/backup/keyvalue/KeyValueBackupTaskTest.java
+++ b/services/robotests/src/com/android/server/backup/keyvalue/KeyValueBackupTaskTest.java
@@ -726,6 +726,39 @@
     }
 
     @Test
+    public void testRunTask_whenSecondAgentUnavailable_commitsFirstAgentState() throws Exception {
+        TransportMock transportMock = setUpInitializedTransport(mTransport);
+        AgentMock agentMock = setUpAgent(PACKAGE_1);
+        setUpAgent(PACKAGE_2.unavailable());
+        agentOnBackupDo(
+                agentMock,
+                (oldState, dataOutput, newState) -> {
+                    writeData(dataOutput, "key", "data".getBytes());
+                    writeState(newState, "newState".getBytes());
+                });
+        KeyValueBackupTask task = createKeyValueBackupTask(transportMock, PACKAGE_1, PACKAGE_2);
+
+        runTask(task);
+
+        assertThat(Files.readAllBytes(getStateFile(mTransport, PACKAGE_1))).isEqualTo(
+                "newState".getBytes());
+    }
+
+    @Test
+    public void testRunTask_whenNonIncrementalAndAgentUnavailable() throws Exception {
+        TransportMock transportMock = setUpInitializedTransport(mTransport);
+        setUpAgent(PACKAGE_1.unavailable());
+        KeyValueBackupTask task = createKeyValueBackupTask(transportMock, true, PACKAGE_1);
+
+        runTask(task);
+
+        verify(mBackupManagerService).setWorkSource(null);
+        verify(mObserver).onResult(PACKAGE_1.packageName, ERROR_AGENT_FAILURE);
+        verify(mObserver).backupFinished(BackupManager.SUCCESS);
+        assertBackupPendingFor(PACKAGE_1);
+    }
+
+    @Test
     public void testRunTask_whenBindToAgentThrowsSecurityException() throws Exception {
         TransportMock transportMock = setUpInitializedTransport(mTransport);
         setUpAgent(PACKAGE_1);
@@ -743,6 +776,23 @@
     }
 
     @Test
+    public void testRunTask_whenNonIncrementalAndBindToAgentThrowsSecurityException() throws Exception {
+        TransportMock transportMock = setUpInitializedTransport(mTransport);
+        setUpAgent(PACKAGE_1);
+        doThrow(SecurityException.class)
+                .when(mBackupManagerService)
+                .bindToAgentSynchronous(argThat(applicationInfo(PACKAGE_1)), anyInt());
+        KeyValueBackupTask task = createKeyValueBackupTask(transportMock, true, PACKAGE_1);
+
+        runTask(task);
+
+        verify(mBackupManagerService).setWorkSource(null);
+        verify(mObserver).onResult(PACKAGE_1.packageName, ERROR_AGENT_FAILURE);
+        verify(mObserver).backupFinished(BackupManager.SUCCESS);
+        assertBackupPendingFor(PACKAGE_1);
+    }
+
+    @Test
     public void testRunTask_whenTransportGetBackupQuotaThrows_notifiesCorrectly() throws Exception {
         TransportMock transportMock = setUpInitializedTransport(mTransport);
         when(transportMock.transport.getBackupQuota(PACKAGE_1.packageName, false))