anchor.diff:     */
     Future<AnalysisResult> getResult(String path) {
       if (!_fsState.hasUri(path)) {
  -      return null;
  +      return new Future.value();
       }
   
       // Return the cached result.
  
positive.code:    */
    Future<CompilationUnitElement> getUnitElement(String path) {
      if (!_fsState.hasUri(path)) {
        return null;
      }
      var completer = new Completer<CompilationUnitElement>();
      _unitElementRequestedFiles
  
negative.code:    */
    Future<AnalysisDriverUnitIndex> getIndex(String path) {
      if (!_fsState.hasUri(path)) {
        return new Future.value();
      }
      var completer = new Completer<AnalysisDriverUnitIndex>();
      _indexRequestedFiles
  