Fix various pub issues.

lib/src/package.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.
 
 library pub.package;
 
 import 'dart:io';
 
 import 'package:barback/barback.dart';
 import 'package:path/path.dart' as p;
@@ skipping 172 matching lines @@
   /// [recursive] is true, this will return all files beneath that path;
   /// otherwise, it will only return files one level beneath it.
   ///
   /// If [useGitIgnore] is passed, this will take the .gitignore rules into
   /// account if the package's root directory is a Git repository.
   ///
   /// Note that the returned paths won't always be beneath [dir]. To safely
   /// convert them to paths relative to the package root, use [relative].
   List<String> listFiles({String beneath, bool recursive: true,
       bool useGitIgnore: false}) {
+    // An in-memory package has no files.
+    if (dir == null) return [];
+
     if (beneath == null) {
       beneath = dir;
     } else {
       beneath = p.join(dir, beneath);
     }
 
     if (!dirExists(beneath)) return [];
 
     // This is used in some performance-sensitive paths and can list many, many
     // files. As such, it leans more havily towards optimization as opposed to
@@ skipping 210 matching lines @@
 
   bool operator ==(other) {
     // TODO(rnystrom): We're assuming here that we don't need to delve into the
     // description.
     return other is PackageDep &&
            other.name == name &&
            other.source == source &&
            other.constraint == constraint;
   }
 }