Fix for issues 3729 and 3523

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

 // Copyright (c) 2011, 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;
 
 /**
  * Represents a Dart 'do/while' statement.
  */
 public class DartDoWhileStatement extends DartStatement {
 
   private DartExpression condition;
   private DartStatement body;
 
   public DartDoWhileStatement(DartExpression condition, DartStatement body) {
     this.condition = becomeParentOf(condition);
     this.body = becomeParentOf(body);
   }
 
   public DartStatement getBody() {
     return body;
   }
 
   public DartExpression getCondition() {
     return condition;
   }
 
   @Override
   public void visitChildren(ASTVisitor<?> visitor) {
-    condition.accept(visitor);
+    if (condition != null) {
+      condition.accept(visitor);
+    }
     body.accept(visitor);
   }
 
   @Override
   public <R> R accept(ASTVisitor<R> visitor) {
     return visitor.visitDoWhileStatement(this);
   }
 }