Issue 3931. Visit children nodes safely.

compiler/java/com/google/dart/compiler/ast/DartMethodDefinition.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 com.google.dart.compiler.resolver.Element;
 import com.google.dart.compiler.resolver.MethodNodeElement;
 
 import java.util.Collections;
 import java.util.List;
@@ skipping 37 matching lines @@
     this.element = (MethodNodeElement) element;
   }
 
   public List<DartInitializer> getInitializers() {
     return Collections.emptyList();
   }
 
   @Override
   public void visitChildren(ASTVisitor<?> visitor) {
     super.visitChildren(visitor);
-    function.accept(visitor);
+    safelyVisitChild(function, visitor);
   }
 
   @Override
   public <R> R accept(ASTVisitor<R> visitor) {
     return visitor.visitMethodDefinition(this);
   }
 
   private static class DartMethodWithInitializersDefinition extends DartMethodDefinition {
 
     private final NodeList<DartInitializer> initializers = NodeList.create(this);
@@ skipping 11 matching lines @@
       return initializers;
     }
 
     @Override
     public void visitChildren(ASTVisitor<?> visitor) {
       super.visitChildren(visitor);
       initializers.accept(visitor);
     }
   }
 }