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

sdk/lib/_internal/compiler/implementation/compile_time_constants.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 dart2js;
 
 /**
  * The [ConstantHandler] keeps track of compile-time constants,
  * initializations of global and static fields, and default values of
  * optional parameters.
@@ skipping 187 matching lines @@
             && value != null
             && element.isField()) {
           DartType elementType = element.computeType(compiler);
           DartType constantType = value.computeType(compiler);
           if (!constantSystem.isSubtype(compiler, constantType, elementType)) {
             if (isConst) {
               compiler.reportFatalError(
                   node, MessageKind.NOT_ASSIGNABLE.error,
                   {'fromType': constantType, 'toType': elementType});
             } else {
-              // If the field can be lazily initialized, we will throw
+              // If the field cannot be lazily initialized, we will throw
               // the exception at runtime.
               value = null;
             }
           }
         }
       }
       if (value != null) {
         initialVariableValues[element] = value;
       } else {
         assert(!isConst);
@@ skipping 743 matching lines @@
           if (fieldValue == null) {
             // Use the default value.
             fieldValue = handler.compileConstant(field);
           }
           jsNewArguments.add(fieldValue);
         },
         includeSuperAndInjectedMembers: true);
     return jsNewArguments;
   }
 }