QString json = "{}";
QJsonDocument jdoc = QJsonDocument::fromJson(json.toUtf8());
QJsonDocument jdoc2;

std::cout << "JSON Documents Loaded" << std::endl;
std::cout << "Document 1: isEmpty: "  << jdoc.isEmpty() << std::endl;
std::cout << "Document 2: isEmpty: "  << jdoc2.isEmpty() << std::endl;

QJsonObject jobj = jdoc.object();
QJsonObject jobj2 = jdoc2.object();

jobj["name"] = "Jimmy";
QJsonObject jSub1;
jSub1["age"] = 12;
jSub1["height"] = "6ft 2in'";
jobj["data"] = jSub1;

QJsonDocument jout = QJsonDocument(jobj);
QJsonDocument jout2 = QJsonDocument(jobj2);
QString sout = QString::fromUtf8(jdoc.toJson(QJsonDocument::JsonFormat::Compact));
QString sout1 = QString::fromUtf8(jout.toJson(QJsonDocument::JsonFormat::Compact));
QString sout2 = QString::fromUtf8(jdoc2.toJson(QJsonDocument::JsonFormat::Compact));
QString sout3 = QString::fromUtf8(jout2.toJson(QJsonDocument::JsonFormat::Compact));

std::cout << "JDOC contents: " << sout.toStdString() <<std::endl;
std::cout << "JOUT contents: " << sout1.toStdString() <<std::endl;
std::cout << "JDOC2 contents: " << sout2.toStdString() <<std::endl;
std::cout << "JOUT2 contents: " << sout3.toStdString() <<std::endl;

--- OUTPUT ---

JSON Documents Loaded
Document 1: isEmpty: 0
Document 2: isEmpty: 1
JDOC contents: {}
JOUT contents: {"data":{"age":12,"height":"6ft 2in'"},"name":"Jimmy"}
JDOC2 contents:
JOUT2 contents: {}