Allow catch part to be optional as in try {} on T [catch (x[,y])] {}

lib/compiler/implementation/scanner/listener.dart

Index: lib/compiler/implementation/scanner/listener.dart
diff --git a/lib/compiler/implementation/scanner/listener.dart b/lib/compiler/implementation/scanner/listener.dart
index 1b549f898e7922fed8a4ff5ae75149c1b1c325a2..da74a9c70226cbfc6b9aad571c0db2899cab3d42 100644
--- a/lib/compiler/implementation/scanner/listener.dart
+++ b/lib/compiler/implementation/scanner/listener.dart
@@ -1429,8 +1429,8 @@ class NodeListener extends ElementListener {
 
   void handleCatchBlock(Token onKeyword, Token catchKeyword) {
     Block block = popNode();
-    NodeList formals = popNode();
-    TypeAnnotation type = onKeyword != null ? popNode() : null;
+    NodeList formals = catchKeyword !== null? popNode(): null;
+    TypeAnnotation type = onKeyword !== null ? popNode() : null;
     pushNode(new CatchBlock(type, formals, block, onKeyword, catchKeyword));
   }