Check for null, when packages dir has no parent.

pkg/analyzer_experimental/lib/src/generated/source_io.dart

 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 library engine.source.io;
 import 'source.dart';
 import 'java_core.dart';
 import 'java_io.dart';
 import 'engine.dart' show AnalysisContext, AnalysisEngine;
 export 'source.dart';
 /**
  * Instances of the class `FileBasedSource` implement a source that represents a file.
@@ skipping 243 matching lines @@
     }
     return new JavaFile.relative(pkgDir, relPath.replaceAll('/', new String.fromCharCode(JavaFile.separatorChar)));
   }
 
   /**
    * @return `true` if "file" was found in "packagesDir", and it is part of the "lib" folder
    *         of the application that contains in this "packagesDir".
    */
   bool isSelfReference(JavaFile packagesDir, JavaFile file) {
     JavaFile rootDir = packagesDir.getParentFile();
+    if (rootDir == null) {
+      return false;
+    }
     String rootPath = rootDir.getAbsolutePath();
     String filePath = file.getAbsolutePath();
     return filePath.startsWith("${rootPath}/lib");
   }
 }
 /**
  * Instances of the class [DirectoryBasedSourceContainer] represent a source container that
  * contains all sources within a given directory.
  *
  * @coverage dart.engine.source
@@ skipping 68 matching lines @@
     }
     return null;
   }
   Source resolveAbsolute(ContentCache contentCache, Uri uri) {
     if (!isFileUri(uri)) {
       return null;
     }
     return new FileBasedSource.con1(contentCache, new JavaFile.fromUri(uri));
   }
 }