Let the inferrer know that lazy variables can also be null incase their initializer throws.

sdk/lib/_internal/compiler/implementation/tree/nodes.dart

 // 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.
 
 part of tree;
 
 abstract class Visitor<R> {
   const Visitor();
 
   R visitNode(Node node);
@@ skipping 156 matching lines @@
   LiteralInt asLiteralInt() => null;
   LiteralList asLiteralList() => null;
   LiteralMap asLiteralMap() => null;
   LiteralMapEntry asLiteralMapEntry() => null;
   LiteralNull asLiteralNull() => null;
   LiteralString asLiteralString() => null;
   MixinApplication asMixinApplication() => null;
   Modifiers asModifiers() => null;
   NamedArgument asNamedArgument() => null;
   NamedMixinApplication asNamedMixinApplication() => null;
+  NewExpression asNewExpression() => null;
   NodeList asNodeList() => null;
   Operator asOperator() => null;
   ParenthesizedExpression asParenthesizedExpression() => null;
   Part asPart() => null;
   PartOf asPartOf() => null;
   Rethrow asRethrow() => null;
   Return asReturn() => null;
   Send asSend() => null;
   SendSet asSendSet() => null;
   Statement asStatement() => null;
@@ skipping 279 matching lines @@
 
 class NewExpression extends Expression {
   /** The token NEW or CONST */
   final Token newToken;
 
   // Note: we expect that send.receiver is null.
   final Send send;
 
   NewExpression([this.newToken, this.send]);
 
+  NewExpression asNewExpression() => this;
+
   accept(Visitor visitor) => visitor.visitNewExpression(this);
 
   visitChildren(Visitor visitor) {
     if (send != null) send.accept(visitor);
   }
 
   bool isConst() {
     return identical(newToken.stringValue, 'const')
         || identical(newToken.stringValue, '@');
   }
@@ skipping 1588 matching lines @@
  * argument).
  *
  * TODO(ahe): This method is controversial, the team needs to discuss
  * if top-level methods are acceptable and what naming conventions to
  * use.
  */
 initializerDo(Node node, f(Node node)) {
   SendSet send = node.asSendSet();
   if (send != null) return f(send.arguments.head);
 }