More documentation (#10589)

diff --git a/packages/flutter_tools/lib/src/android/android_device.dart b/packages/flutter_tools/lib/src/android/android_device.dart
index 59019ab..b4dd532 100644
--- a/packages/flutter_tools/lib/src/android/android_device.dart
+++ b/packages/flutter_tools/lib/src/android/android_device.dart
@@ -476,7 +476,7 @@
 
   static final RegExp _timeRegExp = new RegExp(r'^\d{2}-\d{2} \d{2}:\d{2}:\d{2}\.\d{3}', multiLine: true);
 
-  /// Return the most recent timestamp in the Android log or `null` if there is
+  /// Return the most recent timestamp in the Android log or null if there is
   /// no available timestamp. The format can be passed to logcat's -T option.
   String get lastLogcatTimestamp {
     final String output = runCheckedSync(adbCommandForDevice(<String>[
diff --git a/packages/flutter_tools/lib/src/asset.dart b/packages/flutter_tools/lib/src/asset.dart
index df951e7..6f1e39a 100644
--- a/packages/flutter_tools/lib/src/asset.dart
+++ b/packages/flutter_tools/lib/src/asset.dart
@@ -316,7 +316,7 @@
 /// Given an assetBase location and a pubspec.yaml Flutter manifest, return a
 /// map of assets to asset variants.
 ///
-/// Returns `null` on missing assets.
+/// Returns null on missing assets.
 Map<_Asset, List<_Asset>> _parseAssets(
   PackageMap packageMap,
   Map<String, dynamic> manifestDescriptor,
diff --git a/packages/flutter_tools/lib/src/base/os.dart b/packages/flutter_tools/lib/src/base/os.dart
index b4027ad..1cb5696 100644
--- a/packages/flutter_tools/lib/src/base/os.dart
+++ b/packages/flutter_tools/lib/src/base/os.dart
@@ -27,7 +27,7 @@
   /// Make the given file executable. This may be a no-op on some platforms.
   ProcessResult makeExecutable(File file);
 
-  /// Return the path (with symlinks resolved) to the given executable, or `null`
+  /// Return the path (with symlinks resolved) to the given executable, or null
   /// if `which` was not able to locate the binary.
   File which(String execName) {
     final List<File> result = _which(execName);
@@ -206,7 +206,7 @@
 
 /// Find and return the project root directory relative to the specified
 /// directory or the current working directory if none specified.
-/// Return `null` if the project root could not be found
+/// Return null if the project root could not be found
 /// or if the project root is the flutter repository root.
 String findProjectRoot([String directory]) {
   const String kProjectRootSentinel = 'pubspec.yaml';
diff --git a/packages/flutter_tools/lib/src/commands/build_aot.dart b/packages/flutter_tools/lib/src/commands/build_aot.dart
index 10f79bb..22e0b2c 100644
--- a/packages/flutter_tools/lib/src/commands/build_aot.dart
+++ b/packages/flutter_tools/lib/src/commands/build_aot.dart
@@ -82,7 +82,7 @@
   return fs.path.dirname(packageMap.map[package].toFilePath());
 }
 
-/// Build an AOT snapshot. Return `null` (and log to `printError`) if the method
+/// Build an AOT snapshot. Return null (and log to `printError`) if the method
 /// fails.
 Future<String> buildAotSnapshot(
   String mainPath,
diff --git a/packages/flutter_tools/lib/src/commands/config.dart b/packages/flutter_tools/lib/src/commands/config.dart
index 11f7e07..16c0629 100644
--- a/packages/flutter_tools/lib/src/commands/config.dart
+++ b/packages/flutter_tools/lib/src/commands/config.dart
@@ -42,7 +42,7 @@
       'Analytics reporting is currently ${flutterUsage.enabled ? 'enabled' : 'disabled'}.';
   }
 
-  /// Return `null` to disable tracking of the `config` command.
+  /// Return null to disable tracking of the `config` command.
   @override
   Future<String> get usagePath => null;
 
diff --git a/packages/flutter_tools/lib/src/commands/create.dart b/packages/flutter_tools/lib/src/commands/create.dart
index cf8c3ec..cb60d49 100644
--- a/packages/flutter_tools/lib/src/commands/create.dart
+++ b/packages/flutter_tools/lib/src/commands/create.dart
@@ -311,7 +311,7 @@
   'yaml'
 ]);
 
-/// Return `null` if the project name is legal. Return a validation message if
+/// Return null if the project name is legal. Return a validation message if
 /// we should disallow the project name.
 String _validateProjectName(String projectName) {
   if (!package_names.isValidPackageName(projectName))
@@ -324,7 +324,7 @@
   return null;
 }
 
-/// Return `null` if the project directory is legal. Return a validation message
+/// Return null if the project directory is legal. Return a validation message
 /// if we should disallow the directory name.
 String _validateProjectDir(String dirPath, { String flutterRoot }) {
   if (fs.path.isWithin(flutterRoot, dirPath)) {
diff --git a/packages/flutter_tools/lib/src/dart/analysis.dart b/packages/flutter_tools/lib/src/dart/analysis.dart
index cd20c45..a41dfe4 100644
--- a/packages/flutter_tools/lib/src/dart/analysis.dart
+++ b/packages/flutter_tools/lib/src/dart/analysis.dart
@@ -136,7 +136,7 @@
 
   bool _isFiltered(AnalysisError error) {
     final ErrorProcessor processor = ErrorProcessor.getProcessor(context.analysisOptions, error);
-    // Filtered errors are processed to a severity of `null`.
+    // Filtered errors are processed to a severity of null.
     return processor != null && processor.severity == null;
   }
 
diff --git a/packages/flutter_tools/lib/src/runner/flutter_command.dart b/packages/flutter_tools/lib/src/runner/flutter_command.dart
index eb6984b..28b227e 100644
--- a/packages/flutter_tools/lib/src/runner/flutter_command.dart
+++ b/packages/flutter_tools/lib/src/runner/flutter_command.dart
@@ -134,7 +134,7 @@
     applicationPackages ??= new ApplicationPackageStore();
   }
 
-  /// The path to send to Google Analytics. Return `null` here to disable
+  /// The path to send to Google Analytics. Return null here to disable
   /// tracking of the command.
   Future<String> get usagePath async => name;
 
@@ -218,7 +218,7 @@
   /// Find and return all target [Device]s based upon currently connected
   /// devices and criteria entered by the user on the command line.
   /// If no device can be found that meets specified criteria,
-  /// then print an error message and return `null`.
+  /// then print an error message and return null.
   Future<List<Device>> findAllTargetDevices() async {
     if (!doctor.canLaunchAnything) {
       printError("Unable to locate a development device; please run 'flutter doctor' "
@@ -264,7 +264,7 @@
   /// Find and return the target [Device] based upon currently connected
   /// devices and criteria entered by the user on the command line.
   /// If a device cannot be found that meets specified criteria,
-  /// then print an error message and return `null`.
+  /// then print an error message and return null.
   Future<Device> findTargetDevice() async {
     List<Device> deviceList = await findAllTargetDevices();
     if (deviceList == null)
diff --git a/packages/flutter_tools/lib/src/version.dart b/packages/flutter_tools/lib/src/version.dart
index 4246b61..de68f74 100644
--- a/packages/flutter_tools/lib/src/version.dart
+++ b/packages/flutter_tools/lib/src/version.dart
@@ -236,7 +236,7 @@
   /// This method sends a server request if it's been more than
   /// [kCheckAgeConsideredUpToDate] since the last version check.
   ///
-  /// Returns `null` if the cached version is out-of-date or missing, and we are
+  /// Returns null if the cached version is out-of-date or missing, and we are
   /// unable to reach the server to get the latest version.
   Future<DateTime> _getLatestAvailableFlutterVersion() async {
     Cache.checkLockAcquired();