QQuickWebEngineProfile::defaultProfile() doesn't produce a working profile

Creating a webengine profile using QQuickWebEngineProfile::defaultProfile() creates the class, but reading/writing values in that profile fails without error.

Attached a modified quicknanobrowser example, which creates a profile and prints the current cache dir (which is an empty string instead of the correct cache location).

Afterwards the example tries to set a new cache directory and prints it afterwards again.