Check for null in _getStandardStateLocation().

pkg/analyzer/lib/file_system/physical_file_system.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.
 
 library analyzer.file_system.physical_file_system;
 
 import 'dart:async';
 import 'dart:core';
 import 'dart:io' as io;
 
@@ skipping 34 matching lines @@
 */
 const String _SERVER_DIR = ".dartServer";
 
 /**
  * Returns the path to the user's home directory.
  */
 String _getStandardStateLocation() {
   final home = io.Platform.isWindows
       ? io.Platform.environment['LOCALAPPDATA']
       : io.Platform.environment['HOME'];
-  return io.FileSystemEntity.isDirectorySync(home)
+  return home != null && io.FileSystemEntity.isDirectorySync(home)
       ? join(home, _SERVER_DIR)
       : null;
 }
 
 /**
  * A `dart:io` based implementation of [ResourceProvider].
  */
 class PhysicalResourceProvider implements ResourceProvider {
   static final FileReadMode NORMALIZE_EOL_ALWAYS =
       (String string) => string.replaceAll(new RegExp('\r\n?'), '\n');
@@ skipping 383 matching lines @@
           timer.cancel();
         }
       });
       return completer.future;
     }
     _isSpawning = true;
     _runner = await IsolateRunner.spawn();
     return _runner;
   }
 }