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

lib/compiler/implementation/resolver.dart

Index: lib/compiler/implementation/resolver.dart
diff --git a/lib/compiler/implementation/resolver.dart b/lib/compiler/implementation/resolver.dart
index b1c3710b52f9b888f69b25ceccbc9ef1fd3c1fa7..3f982af889d169fbf52283738f7eb36f1010c77a 100644
--- a/lib/compiler/implementation/resolver.dart
+++ b/lib/compiler/implementation/resolver.dart
@@ -1907,34 +1907,38 @@ class ResolverVisitor extends CommonResolverVisitor<Element> {
   }
 
   visitCatchBlock(CatchBlock node) {
-    // Check that the catch has one or two formal parameters.
-    if (node.formals.isEmpty()) {
-      error(node, MessageKind.EMPTY_CATCH_DECLARATION);
-    } else if (!node.formals.nodes.tail.isEmpty()
-               && !node.formals.nodes.tail.tail.isEmpty()) {
-      for (Node extra in node.formals.nodes.tail.tail) {
-        error(extra, MessageKind.EXTRA_CATCH_DECLARATION);
+    // Check that if catch part is present, then
+    // it has one or two formal parameters.
+    if (node.formals !== null) {
+      if (node.formals.isEmpty()) {
+        error(node, MessageKind.EMPTY_CATCH_DECLARATION);
+      }
+      if (!node.formals.nodes.tail.isEmpty() &&
+          !node.formals.nodes.tail.tail.isEmpty()) {
+        for (Node extra in node.formals.nodes.tail.tail) {
+          error(extra, MessageKind.EXTRA_CATCH_DECLARATION);
+        }
       }
-    }
 
-    // Check that the formals aren't optional and that they have no
-    // modifiers or type.
-    for (Link<Node> link = node.formals.nodes;
-         !link.isEmpty();
-         link = link.tail) {
-      // If the formal parameter is a node list, it means that it is a
-      // sequence of optional parameters.
-      NodeList nodeList = link.head.asNodeList();
-      if (nodeList !== null) {
-        error(nodeList, MessageKind.OPTIONAL_PARAMETER_IN_CATCH);
-      } else {
+      // Check that the formals aren't optional and that they have no
+      // modifiers or type.
+      for (Link<Node> link = node.formals.nodes;
+           !link.isEmpty();
+           link = link.tail) {
+        // If the formal parameter is a node list, it means that it is a
+        // sequence of optional parameters.
+        NodeList nodeList = link.head.asNodeList();
+        if (nodeList !== null) {
+          error(nodeList, MessageKind.OPTIONAL_PARAMETER_IN_CATCH);
+        } else {
         VariableDefinitions declaration = link.head;
-        for (Node modifier in declaration.modifiers.nodes) {
-          error(modifier, MessageKind.PARAMETER_WITH_MODIFIER_IN_CATCH);
-        }
-        TypeAnnotation type = declaration.type;
-        if (type !== null) {
-          error(type, MessageKind.PARAMETER_WITH_TYPE_IN_CATCH);
+          for (Node modifier in declaration.modifiers.nodes) {
+            error(modifier, MessageKind.PARAMETER_WITH_MODIFIER_IN_CATCH);
+          }
+          TypeAnnotation type = declaration.type;
+          if (type !== null) {
+            error(type, MessageKind.PARAMETER_WITH_TYPE_IN_CATCH);
+          }
         }
       }
     }