#include <QJsonArray>
#include <QJsonObject>
#include <QJsonValue>
#include <QDebug>

class Test {
public:
    void initLog()
    {
        QJsonObject log;
        log.insert("demoState", QJsonObject());
        m_log = log;
    }

    void appendState(const QString &key, const QString &state)
    {
        QJsonObject demoState = m_log.value("demoState").toObject();

        // Take object states by key
        QJsonArray states = demoState.contains(key)
                ? demoState.value(key).toArray()
                : QJsonArray();

        // Add new state
        states.append(state);

        qDebug() << "states:" << states;

        // Update states for key
        demoState.insert(key, states);

        qDebug() << "demoState:" << demoState;

        m_log.insert("demoState", demoState);  // <- SIGSEGV when `state == "state2"`
    }

private:
    QJsonObject m_log;
};

int main(int argc, char *argv[])
{
    Q_UNUSED(argc);
    Q_UNUSED(argv);

    Test test;
    test.initLog();

    test.appendState("key1", "state1");
    test.appendState("key2", "state1");

    test.appendState("key1", "state2"); // <- Segmentation fault
    test.appendState("key2", "state2");

    return 0;
}