Issue 3931. Visit children nodes safely.

compiler/java/com/google/dart/compiler/ast/DartParameter.java

Index: compiler/java/com/google/dart/compiler/ast/DartParameter.java
diff --git a/compiler/java/com/google/dart/compiler/ast/DartParameter.java b/compiler/java/com/google/dart/compiler/ast/DartParameter.java
index d15df94469e06a6f5c0116c83565e59906d4dde4..a620a2da3df9131d3bb568a5251c613e4467fbb0 100644
--- a/compiler/java/com/google/dart/compiler/ast/DartParameter.java
+++ b/compiler/java/com/google/dart/compiler/ast/DartParameter.java
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
@@ -88,12 +88,8 @@ public class DartParameter extends DartDeclaration<DartExpression> {
   @Override
   public void visitChildren(ASTVisitor<?> visitor) {
     super.visitChildren(visitor);
-    if (typeNode != null) {
-      typeNode.accept(visitor);
-    }
-    if (defaultExpr != null) {
-      defaultExpr.accept(visitor);
-    }
+    safelyVisitChild(typeNode, visitor);
+    safelyVisitChild(defaultExpr, visitor);
     if (functionParameters != null) {
       functionParameters.accept(visitor);
     }