Check for null in _getStandardStateLocation().

pkg/analyzer/lib/file_system/physical_file_system.dart

Index: pkg/analyzer/lib/file_system/physical_file_system.dart
diff --git a/pkg/analyzer/lib/file_system/physical_file_system.dart b/pkg/analyzer/lib/file_system/physical_file_system.dart
index f997f065b7407f3c5c007414b128dedbac2faf2b..42e85b7727110de0100150f5cc10e56697fe034a 100644
--- a/pkg/analyzer/lib/file_system/physical_file_system.dart
+++ b/pkg/analyzer/lib/file_system/physical_file_system.dart
@@ -52,7 +52,7 @@ 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;
 }