Roster tooltip breaks while appending PEP info

Versions

• OS: Arch Linux
• GTK Version: 3.24.22
• PyGObject Version: 3.36.1
• GLib Version : 2.64.1
• python-nbxmpp Version: 1.0.2
• Gajim Version: 1.2.1

Traceback

Traceback (most recent call last):
  File "/usr/lib/python3.8/site-packages/gajim/roster_window.py", line 5183, in query_tooltip
    value, widget = self._roster_tooltip.get_tooltip(
  File "/usr/lib/python3.8/site-packages/gajim/gtk/tooltips.py", line 267, in get_tooltip
    self._populate_grid(connected_contacts, account, typ)
  File "/usr/lib/python3.8/site-packages/gajim/gtk/tooltips.py", line 373, in _populate_grid
    self._append_pep_info(contact)
  File "/usr/lib/python3.8/site-packages/gajim/gtk/tooltips.py", line 444, in _append_pep_info
    self._ui.tune.set_markup(tune)
TypeError: Argument 1 does not allow None as a value

Steps to reproduce the problem

Use Gajim with unified window layout normally, at some point (possibly when scolling over a username, but just now only by raising focus with a click) an exponentially increasing bunch of popups shows up with above error message. ...