Fixed uninitialized variant in JsonDocument

CHANGELOG.md

@@ -14,6 +14,8 @@ HEAD
 * Added `nesting()` to `JsonArray`, `JsonDocument`, `JsonObject`, and `JsonVariant`
 * Replaced `JsonDocument::nestingLimit` with an additional parameter
   to `deserializeJson()` and `deserializeMsgPack()`
+* Fixed uninitialized variant in `JsonDocument`
+* Added `JsonDocument::isNull()`
 
 > ### BREAKING CHANGES
 > 

src/ArduinoJson/Document/JsonDocument.hpp

@@ -37,6 +37,10 @@ class JsonDocument : public Visitable {
     return getVariant().template is<T>();
   }
 
+  bool isNull() const {
+    return getVariant().isNull();
+  }
+
   size_t memoryUsage() const {
     return _pool.size();
   }
@@ -65,9 +69,13 @@ class JsonDocument : public Visitable {
   }
 
  protected:
-  JsonDocument(MemoryPool pool) : _pool(pool) {}
+  JsonDocument(MemoryPool pool) : _pool(pool) {
+    _data.setNull();
+  }
 
-  JsonDocument(char* buf, size_t capa) : _pool(buf, capa) {}
+  JsonDocument(char* buf, size_t capa) : _pool(buf, capa) {
+    _data.setNull();
+  }
 
   void copy(const JsonDocument& src) {
     to<VariantRef>().set(src.as<VariantRef>());

test/JsonDocument/CMakeLists.txt

@@ -5,6 +5,7 @@
 add_executable(JsonDocumentTests
 	DynamicJsonDocument.cpp
 	nesting.cpp
+	isNull.cpp
 	StaticJsonDocument.cpp
 )
 

test/JsonDocument/isNull.cpp

@@ -0,0 +1,39 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+TEST_CASE("JsonDocument::isNull()") {
+  DynamicJsonDocument doc(4096);
+
+  SECTION("returns true if uninitialized") {
+    REQUIRE(doc.isNull() == true);
+  }
+
+  SECTION("returns false after to<JsonObject>()") {
+    doc.to<JsonObject>();
+    REQUIRE(doc.isNull() == false);
+  }
+
+  SECTION("returns false after to<JsonArray>()") {
+    doc.to<JsonArray>();
+    REQUIRE(doc.isNull() == false);
+  }
+
+  SECTION("returns true after to<JsonVariant>()") {
+    REQUIRE(doc.isNull() == true);
+  }
+
+  SECTION("returns false after set()") {
+    doc.to<JsonVariant>().set(42);
+    REQUIRE(doc.isNull() == false);
+  }
+
+  SECTION("returns true after clear()") {
+    doc.to<JsonObject>();
+    doc.clear();
+    REQUIRE(doc.isNull() == true);
+  }
+}