signals and slots with container types like QHash

[themolecule]

I am having trouble emit()ing a QHash<QString, QVariant> ...

when I do

QHash<QString, QVariant> payload;
payload["variable"]="abc";
 
emit(doCommand(payload));

QHash<QString, QVariant> payload;
payload["variable"]="abc";

emit(doCommand(payload));

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and then

void receiver::doCommand(QHash<QString, QVariant> command)
{
    qDebug() << "The variable was: " << command["variable"].toString();
}

void receiver::doCommand(QHash<QString, QVariant> command)
{
    qDebug() << "The variable was: " << command["variable"].toString();
}

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I end up with an empty string.

Do I have to register the QHash type, or create a typedef, or is the problem that because "payload" in the first piece of code is not a pointer, and therefore can fall out of scope, it is deleted, or perhaps it cannot be passed by value?

It seems that when I emit a signal with a container (or perhaps just a template), the data gets lost.