@Override
    public CodeBlock fromProxy(CodeBlock expression) {
      return CodeBlock.of(
          "$T.ofNullable($L == null ? null : $L)",
          Optional.class,
          expression,
          containedTypeSerializer.fromProxy(expression));
    }
Creates a {@link Serializer} that supports {@link Optional} types.
value/src/main/java/com/google/auto/value/extension/serializable/serializer/impl/OptionalSerializerExtension.java