Check for no constructors before iterating (issue 28703)

pkg/analyzer/lib/src/dart/constant/evaluation.dart

 // Copyright (c) 2014, 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.
 
 library analyzer.src.dart.constant.evaluation;
 
 import 'dart:collection';
 
 import 'package:analyzer/context/declared_variables.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 287 matching lines @@
           // const factory constructors in the SDK, or if the code contains
           // errors (such as delegating to a non-const constructor, or delegating
           // to a constructor that can't be resolved).  In any of these cases,
           // we'll evaluate calls to this constructor without having to refer to
           // any other constants.  So we don't need to report any dependencies.
           return;
         }
         bool defaultSuperInvocationNeeded = true;
         List<ConstructorInitializer> initializers =
             constant.constantInitializers;
-        for (ConstructorInitializer initializer in initializers) {
-          if (initializer is SuperConstructorInvocation ||
-              initializer is RedirectingConstructorInvocation) {
-            defaultSuperInvocationNeeded = false;
+        if (initializers != null) {
+          for (ConstructorInitializer initializer in initializers) {
+            if (initializer is SuperConstructorInvocation ||
+                initializer is RedirectingConstructorInvocation) {
+              defaultSuperInvocationNeeded = false;
+            }
+            initializer.accept(referenceFinder);
           }
-          initializer.accept(referenceFinder);
         }
         if (defaultSuperInvocationNeeded) {
           // No explicit superconstructor invocation found, so we need to
           // manually insert a reference to the implicit superconstructor.
           InterfaceType superclass =
               (constant.returnType as InterfaceType).superclass;
           if (superclass != null && !superclass.isObject) {
             ConstructorElement unnamedConstructor =
                 getConstructorImpl(superclass.element.unnamedConstructor);
             if (unnamedConstructor != null) {
@@ skipping 1760 matching lines @@
   }
 
   @override
   String toString() {
     if (value == null) {
       return "error";
     }
     return value.toString();
   }
 }