Added support for nullptr (closes #998)

test/MixedConfiguration/CMakeLists.txt

@@ -6,12 +6,13 @@
 set(CMAKE_CXX_STANDARD 11)
 
 add_executable(MixedConfigurationTests
+	cpp11.cpp
 	decode_unicode_0.cpp
 	decode_unicode_1.cpp
-	enable_nan_0.cpp
-	enable_nan_1.cpp
 	enable_infinity_0.cpp
 	enable_infinity_1.cpp
+	enable_nan_0.cpp
+	enable_nan_1.cpp
 	use_double_0.cpp
 	use_double_1.cpp
 	use_long_long_0.cpp

test/MixedConfiguration/cpp11.cpp

@@ -0,0 +1,31 @@
+#include <ArduinoJson.h>
+
+#include <catch.hpp>
+
+#if __cplusplus >= 201103L
+
+TEST_CASE("nullptr") {
+  DynamicJsonDocument doc(4096);
+  JsonVariant variant = doc.to<JsonVariant>();
+
+  SECTION("JsonVariant == nullptr") {
+    REQUIRE((variant == nullptr));
+    REQUIRE_FALSE((variant != nullptr));
+  }
+
+  SECTION("JsonVariant != nullptr") {
+    variant.set(42);
+
+    REQUIRE_FALSE((variant == nullptr));
+    REQUIRE((variant != nullptr));
+  }
+
+  SECTION("JsonVariant.set(nullptr)") {
+    variant.set(42);
+    variant.set(nullptr);
+
+    REQUIRE(variant.isNull());
+  }
+}
+
+#endif