Assigning empty object to Q_PROPERTY(QVariantMap...) from QML/JS results in 'Error: Cannot assign null to QVariantMap'

The automatic conversion from JavaScript objects to QVariantMaps fails if the object is empty.

Say you've a Q_PROPERTY of type QVariantMap:

Q_PROPERTY(QVariantMap options READ options WRITE setOptions NOTIFY optionsChanged)

which is exposed to QML/JS. Assigning a different value to 'options' will only work if the JavaScript object isn't empty, e.g.

backend.options = { "one": "two" }

works while

backend.options = {}

results in an exception/error: "Error: Cannot assign null to QVariantMap"