Issue 3931. Visit children nodes safely.

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

-// 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.
 
 package com.google.dart.compiler.ast;
 
 import java.util.List;
 
 /**
  * Represents a Dart 'switch' member ('case' or 'default').
  */
@@ skipping 10 matching lines @@
   public List<DartStatement> getStatements() {
     return statements;
   }
 
   public DartLabel getLabel() {
     return label;
   }
 
   @Override
   public void visitChildren(ASTVisitor<?> visitor) {
-    if (label != null) {
-      label.accept(visitor);
-    }
+    safelyVisitChild(label, visitor);
     statements.accept(visitor);
   }
 }