Issue 3931. Visit children nodes safely.

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

Index: compiler/java/com/google/dart/compiler/ast/DartIfStatement.java
diff --git a/compiler/java/com/google/dart/compiler/ast/DartIfStatement.java b/compiler/java/com/google/dart/compiler/ast/DartIfStatement.java
index 5188120636520a4c366209ba717fcf8a231346d7..ca835611a046c6010a674049dcfd0cc748b3ffba 100644
--- a/compiler/java/com/google/dart/compiler/ast/DartIfStatement.java
+++ b/compiler/java/com/google/dart/compiler/ast/DartIfStatement.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.
 
@@ -33,11 +33,9 @@ public class DartIfStatement extends DartStatement {
 
   @Override
   public void visitChildren(ASTVisitor<?> visitor) {
-    condition.accept(visitor);
-    thenStmt.accept(visitor);
-    if (elseStmt != null) {
-      elseStmt.accept(visitor);
-    }
+    safelyVisitChild(condition, visitor);
+    safelyVisitChild(thenStmt, visitor);
+    safelyVisitChild(elseStmt, visitor);
   }
 
   @Override