Add nullptr_t

src/ArduinoJson/Polyfills/utility.hpp

@@ -8,6 +8,8 @@
 
 ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 
+using nullptr_t = decltype(nullptr);
+
 template <class T>
 T&& forward(typename remove_reference<T>::type& t) noexcept {
   return static_cast<T&&>(t);

src/ArduinoJson/Variant/ConverterImpl.hpp

@@ -6,6 +6,7 @@
 
 #include <ArduinoJson/Json/JsonSerializer.hpp>
 #include <ArduinoJson/Memory/StringBuilder.hpp>
+#include <ArduinoJson/Polyfills/utility.hpp>
 #include <ArduinoJson/Variant/JsonVariantConst.hpp>
 
 ARDUINOJSON_BEGIN_PUBLIC_NAMESPACE
@@ -174,11 +175,11 @@ struct Converter<SerializedValue<T>> : private detail::VariantAttorney {
 };
 
 template <>
-struct Converter<decltype(nullptr)> : private detail::VariantAttorney {
+struct Converter<detail::nullptr_t> : private detail::VariantAttorney {
-  static void toJson(decltype(nullptr), JsonVariant dst) {
+  static void toJson(detail::nullptr_t, JsonVariant dst) {
     detail::VariantData::setNull(getData(dst), getResourceManager(dst));
   }
-  static decltype(nullptr) fromJson(JsonVariantConst) {
+  static detail::nullptr_t fromJson(JsonVariantConst) {
     return nullptr;
   }
   static bool checkJson(JsonVariantConst src) {

src/ArduinoJson/Variant/VariantCompare.hpp

@@ -7,6 +7,7 @@
 #include <ArduinoJson/Configuration.hpp>
 #include <ArduinoJson/Numbers/arithmeticCompare.hpp>
 #include <ArduinoJson/Polyfills/type_traits.hpp>
+#include <ArduinoJson/Polyfills/utility.hpp>
 #include <ArduinoJson/Strings/StringAdapters.hpp>
 #include <ArduinoJson/Variant/JsonVariantVisitor.hpp>
 
@@ -74,8 +75,8 @@ struct NullComparer : ComparerBase {
 };
 
 template <>
-struct Comparer<decltype(nullptr), void> : NullComparer {
+struct Comparer<nullptr_t, void> : NullComparer {
-  explicit Comparer(decltype(nullptr)) : NullComparer() {}
+  explicit Comparer(nullptr_t) : NullComparer() {}
 };
 
 struct ArrayComparer : ComparerBase {