Make pub strong-mode clean.

lib/src/command/deps.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:collection';
 
 import '../ascii_tree.dart' as tree;
 import '../command.dart';
 import '../log.dart' as log;
 import '../package.dart';
@@ skipping 126 matching lines @@
   /// Generates a dependency tree for the root package.
   ///
   /// If a package is encountered more than once (i.e. a shared or circular
   /// dependency), later ones are not traversed. This is done in breadth-first
   /// fashion so that a package will always be expanded at the shallowest
   /// depth that it appears at.
   void _outputTree() {
     // The work list for the breadth-first traversal. It contains the package
     // being added to the tree, and the parent map that will receive that
     // package.
-    var toWalk = new Queue<Pair<Package, Map>>();
+    var toWalk = new Queue<Pair<Package, Map<String, Map>>>();
     var visited = new Set<String>.from([entrypoint.root.name]);
 
     // Start with the root dependencies.
-    var packageTree = {};
+    var packageTree = <String, Map>{};
     var immediateDependencies = entrypoint.root.immediateDependencies.toSet();
     if (!_includeDev) {
       immediateDependencies.removeAll(entrypoint.root.devDependencies);
     }
     for (var dep in immediateDependencies) {
       toWalk.add(new Pair(_getPackage(dep.name), packageTree));
     }
 
     // Do a breadth-first walk to the dependency graph.
     while (toWalk.isNotEmpty) {
       var pair = toWalk.removeFirst();
       var package = pair.first;
       var map = pair.last;
 
       if (visited.contains(package.name)) {
         map[log.gray('${package.name}...')] = {};
         continue;
       }
 
       visited.add(package.name);
 
       // Populate the map with this package's dependencies.
-      var childMap = {};
+      var childMap = <String, Map>{};
       map[_labelPackage(package)] = childMap;
 
       for (var dep in package.dependencies) {
         toWalk.add(new Pair(_getPackage(dep.name), childMap));
       }
     }
 
     _buffer.write(tree.fromMap(packageTree, showAllChildren: true));
   }
 
@@ skipping 29 matching lines @@
   /// available.
   ///
   /// It's very unlikely that the lockfile won't be up-to-date with the pubspec,
   /// but it's possible, since [Entrypoint.assertUpToDate]'s modification time
   /// check can return a false negative. This fails gracefully if that happens.
   Package _getPackage(String name) {
     var package = entrypoint.packageGraph.packages[name];
     if (package != null) return package;
     dataError('The pubspec.yaml file has changed since the pubspec.lock file '
         'was generated, please run "pub get" again.');
+    return null;
   }
 }