Steps to reproduce:

Printer HP Envy 5530 connected via LAN

1 Open hp-toolbox
2 Right-click on "HP Envy 5530 Series" -> "Scan..."

=> nothing happens, except hourglass spinning

If hp-toolbox started with "--debug", terminal window shows

> hp-toolbox(UI)[7367]: debug: updateDevice(hp:/net/ENVY_5530_series?zc=HP3464A9E628B4)
> hp-toolbox(UI)[7367]: debug: updateCurrentTab()
> hp-toolbox(UI)[7367]: debug: Run: ******************** /usr/bin/xsane -V %SANE_URI% (hp:/net/ENVY_5530_series?zc=HP3464A9E628B4) ********************
> hp-toolbox(UI)[7367]: debug: /usr/bin/xsane -V %SANE_URI%
> Traceback (most recent call last):
>  File "/usr/share/hplip/ui4/devmgr5.py", line 907, in <lambda>
>    popup.addAction(self.__tr("Scan..."),  lambda: self.contextMenuFunc(self.user_settings.cmd_scan)) #self.ScanButton_clicked)
>  File "/usr/share/hplip/ui4/devmgr5.py", line 946, in contextMenuFunc
    self.runExternalCommand(f)
>  File "/usr/share/hplip/ui4/devmgr5.py", line 2166, in runExternalCommand
    for x in cmd.split(macro_char)])
> TypeError: sequence item 0: expected string, QString found

This does NOT happen when clicking "Scan" in the "Actions" tab in the main
window of hp-toolbox:

hp-toolbox(UI)[9026]: debug: Run: ******************** /usr/bin/xsane -V
%SANE_URI% (hp:/net/ENVY_5530_series?zc=HP3464A9E628B4) ********************
hp-toolbox(UI)[9026]: debug: /usr/bin/xsane -V %SANE_URI%
hp-toolbox(UI)[9026]: debug: /usr/bin/xsane -V
hpaio:/net/ENVY_5530_series?zc=HP3464A9E628B4
hp-toolbox(UI)[9026]: debug: /usr/bin/xsane
hp-toolbox(UI)[9026]: debug: ['/usr/bin/xsane', '-V',
'hpaio:/net/ENVY_5530_series?zc=HP3464A9E628B4']