Change analysis server protocol to omit empty lists when optional.

pkg/analysis_server/lib/src/search/search_result.dart

Index: pkg/analysis_server/lib/src/search/search_result.dart
diff --git a/pkg/analysis_server/lib/src/search/search_result.dart b/pkg/analysis_server/lib/src/search/search_result.dart
index 7e08d5f3c99346dade2ef62551b952158095fc6f..e5cff3b1815b913c0fec3acfab786a7c4830fe3c 100644
--- a/pkg/analysis_server/lib/src/search/search_result.dart
+++ b/pkg/analysis_server/lib/src/search/search_result.dart
@@ -17,7 +17,7 @@ SearchResult searchResultFromMatch(SearchMatch match) {
           match.sourceRange.offset,
           match.sourceRange.length);
   List<Element> path = _computePath(match.element);
-  return new SearchResult(location, kind, !match.isResolved, path);
+  return new SearchResult(location, kind, !match.isResolved, path: path);
 }
 
 List<Element> _computePath(engine.Element element) {