Slim down `ndncert-common.hpp`
Change-Id: Ifba0966d3787c5cbf770963b82cba054ee1fe791
diff --git a/src/detail/probe-encoder.hpp b/src/detail/probe-encoder.hpp
index bd15463..815a840 100644
--- a/src/detail/probe-encoder.hpp
+++ b/src/detail/probe-encoder.hpp
@@ -1,6 +1,6 @@
/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
/*
- * Copyright (c) 2017-2022, Regents of the University of California.
+ * Copyright (c) 2017-2024, Regents of the University of California.
*
* This file is part of ndncert, a certificate management system based on NDN.
*
@@ -23,6 +23,8 @@
#include "detail/ndncert-common.hpp"
+#include <optional>
+
namespace ndncert::probetlv {
// For Client use