| Index: pkg/serialization/lib/src/reader_writer.dart
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| diff --git a/pkg/serialization/lib/src/reader_writer.dart b/pkg/serialization/lib/src/reader_writer.dart
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| index b40196e87c4ab058ad8b40d9b9d4c742f036254e..920318555b2e00774d5aed8e74b81fb517f707e7 100644
 | 
| --- a/pkg/serialization/lib/src/reader_writer.dart
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| +++ b/pkg/serialization/lib/src/reader_writer.dart
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| @@ -40,7 +40,7 @@ class Writer implements ReaderOrWriter {
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|     * but also serves to record which objects we have already seen.
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|     */
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|    final Map<dynamic, Reference> references =
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| -      new IdentityMap<Object, Reference>();
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| +      new HashMap<Object, Reference>(equals: identical);
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|  
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|    /**
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|     * The state of objects that need to be serialized is stored here.
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| 
 |