QAudioSource without explicitly specified QAudioFormat is not functional

QAudioSource without explicitly specified QAudioFormat is not functional at least with "darwin" multimedia backend on macOS. But I suppose this might be relevant for other platforms and other backends.

Details:
According to the documentation and public API, QAudioSource has constructors with
defaulted QAudioFormat argument.

https://doc.qt.io/qt-6/qaudiosource.html#QAudioSource

public:
    explicit QAudioSource(const QAudioFormat &format = QAudioFormat(), QObject *parent = nullptr);
    explicit QAudioSource(const QAudioDevice &audioDeviceInfo, const QAudioFormat &format = QAudioFormat(), QObject *parent = nullptr);

Usually the "default" argument means something optional. Moreover there is no any method to set a format after the construction. So I expect that when I instantiate QAudioSource and don't explicitly specify the format, it will still be functional and will use e.g. QAudioDevice::preferredFormat() under the hood.

But, at least on "darwin" backend, it just fails silently at QAudioSource::start()

see

QDarwinAudioSource::start(QIODevice *device)
{
    QIODevice* op = device;

    if (!m_audioDeviceInfo.isFormatSupported(m_audioFormat) || !open()) {
        m_stateCode = QAudio::StoppedState;
        m_errorCode = QAudio::OpenError;
        return;  // <<<< just fails silently when m_audioFormat is null
    }
...
}