From 269227f6bd7d4cf40bb2308d14e7f8a74001b449 Mon Sep 17 00:00:00 2001
From: dota17 <chenguopingdota@163.com>
Date: Wed, 15 Jul 2020 09:22:08 +0800
Subject: [PATCH] fix issue590: add the support to null type for
 as<std::string>

---
 include/yaml-cpp/node/impl.h        | 4 ++++
 test/integration/load_node_test.cpp | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/include/yaml-cpp/node/impl.h b/include/yaml-cpp/node/impl.h
index 06a4884..7065404 100644
--- a/include/yaml-cpp/node/impl.h
+++ b/include/yaml-cpp/node/impl.h
@@ -110,6 +110,8 @@ struct as_if<std::string, S> {
   const Node& node;
 
   std::string operator()(const S& fallback) const {
+    if (node.Type() == NodeType::Null)
+      return "null";
     if (node.Type() != NodeType::Scalar)
       return fallback;
     return node.Scalar();
@@ -138,6 +140,8 @@ struct as_if<std::string, void> {
   const Node& node;
 
   std::string operator()() const {
+    if (node.Type() == NodeType::Null)
+      return "null";
     if (node.Type() != NodeType::Scalar)
       throw TypedBadConversion<std::string>(node.Mark());
     return node.Scalar();
diff --git a/test/integration/load_node_test.cpp b/test/integration/load_node_test.cpp
index 8f3bece..d0bbd4b 100644
--- a/test/integration/load_node_test.cpp
+++ b/test/integration/load_node_test.cpp
@@ -314,6 +314,8 @@ TEST(NodeTest, IncorrectFlow) {
 TEST(NodeTest, LoadTildeAsNull) {
   Node node = Load("~");
   ASSERT_TRUE(node.IsNull());
+  EXPECT_EQ(node.as<std::string>(), "null");
+  EXPECT_EQ(node.as<std::string>("~"), "null");
 }
 
 TEST(NodeTest, LoadNullWithStrTag) {