util: backport optional::reset

refs #3753

Change-Id: I17e77d7b7e3c450fc86aec06f5c2d3ecfcc1444a
diff --git a/tests/unit-tests/util/backports.t.cpp b/tests/unit-tests/util/backports.t.cpp
index 3722834..629c3ee 100644
--- a/tests/unit-tests/util/backports.t.cpp
+++ b/tests/unit-tests/util/backports.t.cpp
@@ -226,6 +226,13 @@
   BOOST_CHECK_EQUAL(static_cast<bool>(o2), false);
 }
 
+BOOST_AUTO_TEST_CASE(Reset)
+{
+  optional<int> o1(1);
+  o1.reset();
+  BOOST_CHECK_EQUAL(static_cast<bool>(o1), false);
+}
+
 BOOST_AUTO_TEST_CASE(Emplace)
 {
   optional<std::pair<int, int>> o1;