It's 2021, and this issue still exists.
In my case with qdbus command, installing and re-installing qt5-default does
not help.
The solution of @yatsek worked:
qdbus: could not find a Qt installation of ''
$ sudo apt-get install apt-file
$ sudo apt-file update
$ apt-file search
Hello
This bug seems to be fixed in KDE 4.2 (the default values are correct),
which sould be backported to Intrepid soon. If you still experience this
bug after updating, please reopen this bug report.
** Changed in: kdepim (Ubuntu)
Status: Confirmed = Fix Released
** Changed in: kdepim
