Fix null reference issues in bazel.dart.

pkg/analyzer/lib/src/generated/bazel.dart

 // Copyright (c) 2016, 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.src.generated.bazel;
 
 import 'dart:core';
 
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/src/generated/source.dart';
@@ skipping 73 matching lines @@
     if (!context.isAbsolute(path)) {
       throw new ArgumentError('not absolute: $path');
     }
     path = context.normalize(path);
 
     Folder folder = provider.getFolder(path);
     while (true) {
       Folder parent = folder.parent;
 
       // Found the READONLY folder, must be a git-based workspace.
-      if (readonlySuffix != null) {
+      if (readonlySuffix != null && parent != null) {
         Folder readonlyFolder = parent.getChildAssumingFolder(_READONLY);
-        if (parent != null && readonlyFolder.exists) {
+        if (readonlyFolder.exists) {
           String root = folder.path;
           String readonly = readonlyFolder.path;
           return new BazelWorkspace._(
               provider,
               root,
               context.join(readonly, readonlySuffix),
               context.join(root, '$symlinkPrefix-bin'),
               context.join(root, '$symlinkPrefix-genfiles'));
         }
       }
 
       // Found the WORKSPACE file, must be a non-git workspace.
       if (folder.getChildAssumingFile(_WORKSPACE).exists) {
         String root = folder.path;
         return new BazelWorkspace._(
             provider,
             root,
             null,
             context.join(root, '$symlinkPrefix-bin'),
             context.join(root, '$symlinkPrefix-genfiles'));
       }
 
       // Go up the folder.
       folder = parent;
       if (folder == null) {
-        return null;
+        return new BazelWorkspace._(provider, path, null, null, null);
       }
     }
   }
 
   BazelWorkspace._(
       this.provider, this.root, this.readonly, this.bin, this.genfiles);
 
   /**
    * Return the file with the given [absolutePath], looking first into
    * directories for generated files: `bazel-bin` and `bazel-genfiles`, and
    * then into the workspace root. The file in the workspace root is returned
    * even if it does not exist. Return `null` if the given [absolutePath] is
    * not in the workspace [root].
    */
   File findFile(String absolutePath) {
     Context context = provider.pathContext;
     try {
       String relative = context.relative(absolutePath, from: root);
       // genfiles
-      {
+      if (genfiles != null) {
         File file = provider.getFile(context.join(genfiles, relative));
         if (file.exists) {
           return file;
         }
       }
       // bin
-      {
+      if (bin != null) {
         File file = provider.getFile(context.join(bin, relative));
         if (file.exists) {
           return file;
         }
       }
       // READONLY
       if (readonly != null) {
         File file = provider.getFile(context.join(readonly, relative));
         if (file.exists) {
           return file;
         }
       }
       // Not generated, return the default one.
       return provider.getFile(absolutePath);
     } catch (_) {
       return null;
     }
   }
 }