Handle case where lastLogcatTimestamp is null (#45937)

packages/flutter_tools/lib/src/android/android_device.dart

@@ -1009,7 +1009,13 @@ class _AdbLogReader extends DeviceLogReader {
   void _start() {
     final String lastTimestamp = device.lastLogcatTimestamp;
     // Start the adb logcat process and filter the most recent logs since `lastTimestamp`.
-    final List<String> args = <String>['logcat', '-v', 'time', '-T', lastTimestamp];
+    final List<String> args = <String>[
+      'logcat',
+      '-v',
+      'time',
+      '-T',
+      lastTimestamp ?? '', // Empty `-T` means the timestamp of the logcat command invocation.
+    ];
     processUtils.start(device.adbCommandForDevice(args)).then<void>((Process process) {
       _process = process;
       // We expect logcat streams to occasionally contain invalid utf-8,

packages/flutter_tools/test/general.shard/android/android_device_test.dart

@@ -707,6 +707,24 @@ flutter:
       AndroidSdk: () => mockAndroidSdk,
       ProcessManager: () => mockProcessManager,
     });
+
+    testUsingContext('calls adb logcat with expected flags when the device logs are empty', () async {
+      when(mockAndroidSdk.adbPath).thenReturn('adb');
+      when(mockProcessManager.runSync(<String>['adb', '-s', '1234', 'shell', '-x', 'logcat', '-v', 'time', '-t', '1']))
+        .thenReturn(ProcessResult(0, 0, '', ''));
+      when(mockProcessManager.start(argThat(contains('logcat'))))
+        .thenAnswer((_) => Future<Process>.value(createMockProcess()));
+
+      final AndroidDevice device = AndroidDevice('1234');
+      final DeviceLogReader logReader = device.getLogReader();
+      logReader.logLines.listen((_) {});
+
+      verify(mockProcessManager.start(const <String>['adb', '-s', '1234', 'logcat', '-v', 'time', '-T', '']))
+        .called(1);
+    }, overrides: <Type, Generator>{
+      AndroidSdk: () => mockAndroidSdk,
+      ProcessManager: () => mockProcessManager,
+    });
   });
 
   test('Can parse adb shell dumpsys info', () {