Ignore non-UTF8 strings in the environment

sdk/lib/io/platform_impl.dart

 // Copyright (c) 2012, 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.
 
 part of dart.io;
 
 class _Platform {
   external static int _numberOfProcessors();
   external static String _pathSeparator();
   external static String _operatingSystem();
@@ skipping 48 matching lines @@
 
   static Map<String, String> get environment {
     if (_environmentCache == null) {
       var env = _environment();
       if (env is !OSError) {
         var isWindows = operatingSystem == 'windows';
         var result = isWindows
             ? new _CaseInsensitiveStringMap<String>()
             : new Map<String, String>();
         for (var str in env) {
+          if (str == null) {
+            continue;
+          }
           // The Strings returned by [_environment()] are expected to be
           // valid environment entries, but exceptions have been seen
           // (e.g., an entry of just '=' has been seen on OS/X).
           // Invalid entries (lines without a '=' or with an empty name)
           // are discarded.
           var equalsIndex = str.indexOf('=');
           if (equalsIndex > 0) {
             result[str.substring(0, equalsIndex)] =
                 str.substring(equalsIndex + 1);
           }
@@ skipping 35 matching lines @@
   V remove(Object key) => key is String ? _map.remove(key.toUpperCase()) : null;
   void clear() { _map.clear(); }
   void forEach(void f(String key, V value)) { _map.forEach(f); }
   Iterable<String> get keys => _map.keys;
   Iterable<V> get values => _map.values;
   int get length => _map.length;
   bool get isEmpty => _map.isEmpty;
   bool get isNotEmpty => _map.isNotEmpty;
   String toString() => _map.toString();
 }