use null aware operators (#32711) * use null aware operators * rollback changes about null-aware operator * disable lint prefer_is_not_empty

diff --git a/packages/flutter_tools/lib/src/base/config.dart b/packages/flutter_tools/lib/src/base/config.dart
index 388e989..b3a505d 100644
--- a/packages/flutter_tools/lib/src/base/config.dart
+++ b/packages/flutter_tools/lib/src/base/config.dart

@@ -46,6 +46,5 @@
 
 String _userHomeDir() {
   final String envKey = platform.operatingSystem == 'windows' ? 'APPDATA' : 'HOME';
-  final String value = platform.environment[envKey];
-  return value == null ? '.' : value;
+  return platform.environment[envKey] ?? '.';
 }

diff --git a/packages/flutter_tools/lib/src/ios/simulators.dart b/packages/flutter_tools/lib/src/ios/simulators.dart
index 428e154..5fed6ac 100644
--- a/packages/flutter_tools/lib/src/ios/simulators.dart
+++ b/packages/flutter_tools/lib/src/ios/simulators.dart

@@ -288,7 +288,7 @@
     if (isSupported())
       return 'Supported';
 
-    return _supportMessage != null ? _supportMessage : 'Unknown';
+    return _supportMessage ?? 'Unknown';
   }
 
   @override

diff --git a/packages/flutter_tools/lib/src/test/event_printer.dart b/packages/flutter_tools/lib/src/test/event_printer.dart
index dee2d00..a3f4cc1 100644
--- a/packages/flutter_tools/lib/src/test/event_printer.dart
+++ b/packages/flutter_tools/lib/src/test/event_printer.dart

@@ -8,7 +8,7 @@
 
 /// Prints JSON events when running a test in --machine mode.
 class EventPrinter extends TestWatcher {
-  EventPrinter({StringSink out}) : _out = out == null ? stdout: out;
+  EventPrinter({StringSink out}) : _out = out ?? stdout;
 
   final StringSink _out;
 

diff --git a/packages/flutter_tools/lib/src/version.dart b/packages/flutter_tools/lib/src/version.dart
index b2ef9c4..6d1503f 100644
--- a/packages/flutter_tools/lib/src/version.dart
+++ b/packages/flutter_tools/lib/src/version.dart

@@ -105,7 +105,7 @@
   @override
   String toString() {
     final String versionText = frameworkVersion == 'unknown' ? '' : ' $frameworkVersion';
-    final String flutterText = 'Flutter$versionText • channel $channel • ${repositoryUrl == null ? 'unknown source' : repositoryUrl}';
+    final String flutterText = 'Flutter$versionText • channel $channel • ${repositoryUrl ?? 'unknown source'}';
     final String frameworkText = 'Framework • revision $frameworkRevisionShort ($frameworkAge) • $frameworkCommitDate';
     final String engineText = 'Engine • revision $engineRevisionShort';
     final String toolsText = 'Tools • Dart $dartSdkVersion';

diff --git a/packages/flutter_tools/lib/src/vmservice.dart b/packages/flutter_tools/lib/src/vmservice.dart
index 4290f6b..6ba3677 100644
--- a/packages/flutter_tools/lib/src/vmservice.dart
+++ b/packages/flutter_tools/lib/src/vmservice.dart

@@ -718,13 +718,11 @@
 
   /// The number of bytes allocated (e.g. by malloc) in the native heap.
   int _heapAllocatedMemoryUsage;
-  int get heapAllocatedMemoryUsage {
-    return _heapAllocatedMemoryUsage == null ? 0 : _heapAllocatedMemoryUsage;
-  }
+  int get heapAllocatedMemoryUsage => _heapAllocatedMemoryUsage ?? 0;
 
   /// The peak resident set size for the process.
   int _maxRSS;
-  int get maxRSS => _maxRSS == null ? 0 : _maxRSS;
+  int get maxRSS => _maxRSS ?? 0;
 
   // The embedder's name, Flutter or dart_runner.
   String _embedder;