anchor.diff:        var offset = offsetFromPosition(_files[path], position);
         var id =
             (await _server.search.findElementReferences(path, offset, true)).id;
  -      if (id == null) return null;
  +      if (id == null) return const [];
         var references =
             (_searchResults[id] = new Completer<List<Location>>()).future;
         if (context.includeDeclaration) {
  
positive.code:     return _pools.lock(path, () async {
        var offset = offsetFromPosition(_files[path], position);
        var id = (await _server.completion.getSuggestions(path, offset)).id;
        if (id == null) {
          return new CompletionList((b) => b
            ..isIncomplete = false
            ..items = const []);
        }
        _completionPaths[id] = path;
        return (_completions[id] = new Completer<CompletionList>()).future;
      });
  
negative.code:       var offset = offsetFromPosition(_files[path], position);
        var id =
            (await _server.search.findElementReferences(path, offset, false)).id;
        if (id == null) return const [];
        var completer = new Completer<List<DocumentHighlight>>();
        _highlightResults[id] = (searchResults) =>
            completer.complete(_toHighlightList(searchResults, path, _files));
  