tlv: introduce NullSignature signature type

Refs: #4900
Change-Id: Ib5ab76e1e7a4b0cbec09b945859fb30e9322dd6b
diff --git a/tests/unit/encoding/tlv.t.cpp b/tests/unit/encoding/tlv.t.cpp
index 478fd83..1acffa5 100644
--- a/tests/unit/encoding/tlv.t.cpp
+++ b/tests/unit/encoding/tlv.t.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2013-2019 Regents of the University of California.
+ * Copyright (c) 2013-2020 Regents of the University of California.
  *
  * This file is part of ndn-cxx library (NDN C++ library with eXperimental eXtensions).
  *
@@ -569,7 +569,7 @@
 
 BOOST_AUTO_TEST_SUITE_END() // NonNegativeInteger
 
-BOOST_AUTO_TEST_SUITE(PrintHelpers)
+BOOST_AUTO_TEST_SUITE(OutputOperators)
 
 BOOST_AUTO_TEST_CASE(PrintSignatureTypeValue)
 {
@@ -579,7 +579,9 @@
   BOOST_CHECK_EQUAL(boost::lexical_cast<std::string>(SignatureSha256WithEcdsa), "SignatureSha256WithEcdsa");
   BOOST_CHECK_EQUAL(boost::lexical_cast<std::string>(SignatureHmacWithSha256), "SignatureHmacWithSha256");
   BOOST_CHECK_EQUAL(boost::lexical_cast<std::string>(static_cast<SignatureTypeValue>(5)), "Unknown(5)");
-  BOOST_CHECK_EQUAL(boost::lexical_cast<std::string>(static_cast<SignatureTypeValue>(200)), "Unknown(200)");
+  BOOST_CHECK_EQUAL(boost::lexical_cast<std::string>(static_cast<SignatureTypeValue>(199)), "Unknown(199)");
+  BOOST_CHECK_EQUAL(boost::lexical_cast<std::string>(NullSignature), "NullSignature");
+  BOOST_CHECK_EQUAL(boost::lexical_cast<std::string>(static_cast<SignatureTypeValue>(201)), "Unknown(201)");
 }
 
 BOOST_AUTO_TEST_CASE(PrintContentTypeValue)
@@ -601,7 +603,7 @@
   BOOST_CHECK_EQUAL(boost::lexical_cast<std::string>(static_cast<ContentTypeValue>(19910118)), "Unknown(19910118)");
 }
 
-BOOST_AUTO_TEST_SUITE_END() // PrintHelpers
+BOOST_AUTO_TEST_SUITE_END() // OutputOperators
 
 BOOST_AUTO_TEST_SUITE_END() // TestTlv
 BOOST_AUTO_TEST_SUITE_END() // Encoding
diff --git a/tests/unit/face.t.cpp b/tests/unit/face.t.cpp
index ef1cab3..b368667 100644
--- a/tests/unit/face.t.cpp
+++ b/tests/unit/face.t.cpp
@@ -426,14 +426,14 @@
 
   BOOST_CHECK_EQUAL(face.sentNacks.size(), 0);
 
-  face.put(makeNack(*makeInterest("/unsolicited", false, DEFAULT_INTEREST_LIFETIME, 18645250),
+  face.put(makeNack(*makeInterest("/unsolicited", false, nullopt, 18645250),
                     lp::NackReason::NO_ROUTE));
   advanceClocks(10_ms);
   BOOST_CHECK_EQUAL(face.sentNacks.size(), 0); // unsolicited Nack would not be sent
 
-  auto interest1 = makeInterest("/Hello/World", false, DEFAULT_INTEREST_LIFETIME, 14247162);
+  auto interest1 = makeInterest("/Hello/World", false, nullopt, 14247162);
   face.receive(*interest1);
-  auto interest2 = makeInterest("/another/prefix", false, DEFAULT_INTEREST_LIFETIME, 92203002);
+  auto interest2 = makeInterest("/another/prefix", false, nullopt, 92203002);
   face.receive(*interest2);
   advanceClocks(10_ms);
 
@@ -464,7 +464,7 @@
   face.setInterestFilter("/", bind([&] { hasInterest2 = true; }));
   advanceClocks(10_ms);
 
-  auto interest = makeInterest("/A", false, DEFAULT_INTEREST_LIFETIME, 14333271);
+  auto interest = makeInterest("/A", false, nullopt, 14333271);
   face.receive(*interest);
   advanceClocks(10_ms);
   BOOST_CHECK(hasInterest1);
@@ -495,7 +495,7 @@
   face.setInterestFilter(InterestFilter("/").allowLoopback(false),
     bind([] { BOOST_ERROR("Unexpected Interest on second InterestFilter"); }));
 
-  auto interest = makeInterest("/A", false, DEFAULT_INTEREST_LIFETIME, 28395852);
+  auto interest = makeInterest("/A", false, nullopt, 28395852);
   face.expressInterest(*interest,
                        bind([] { BOOST_FAIL("Unexpected data"); }),
                        [&] (const Interest&, const lp::Nack& nack) {