Force Qutebrowser to close tab and open default one when there is one tab in the window

In Qutebrowser, I try to create the following behavior: tab-close, or at least the action associated with it (i.e., pressing d), should, in all situations where more than one tab is open, close the current tab, as it already does. However, if the window contains only one tab, it should close that tab and open the default tab in its place. Basically, like Firefox does. I made many tries in config.py, creating a smart_tab_close() function which gets the number of opened tabs, but I failed. So how to make Qutebrowser act like that?