What/Why QDbusConnection thread?

[Tuyen]

I created a QtQuick application and ran it in docker environment. Right after the application is launched, I saw following message:

The last reference on a connection was dropped without closing the connection. This is a bug in an application. See dbus_connection_unref() documentation for details.

I inspected the application and saw there is a thread called QDbusConnection is running inside application's process even my project was not configured with QT += dbus.

I don't know what is the thread and why did it present?