incremental progress on Value

frog/lib/corelib_impl.dart

Index: frog/lib/corelib_impl.dart
diff --git a/frog/lib/corelib_impl.dart b/frog/lib/corelib_impl.dart
index e08e38c59950532fc4da9255666a21dee20e270f..0950eefb183cca663c0ac90e72fb6778632fc10b 100644
--- a/frog/lib/corelib_impl.dart
+++ b/frog/lib/corelib_impl.dart
@@ -254,7 +254,7 @@ class JSSyntaxRegExp implements RegExp {
 
   String stringMatch(String str) {
     var match = firstMatch(str);
-    return match && match.group(0);
+    return match === null ? null : match.group(0);
   }
 
   Iterable<Match> allMatches(String str) => new _AllMatchesIterable(this, str);