sync fails: Synchronization failed with the following exception: Unexpected DTD declaration. Line 6, position 3.

[Johannes Rohr]

as of the latest version, sync fails, including to a local folder, webdav or a tomboy (grauphel) server: I see the same on Debian Buster

Unhandled Exception:
System.NullReferenceException: Object reference not set to an instance of an object
  at Tomboy.GnomeApplication.OnExitSignal (System.Int32 signal) [0x00001] in <f9cba0df4a314f279ace0200385e99c2>:0
  at (wrapper managed-to-native) Gtk.Application:gtk_main ()
  at Gtk.Application.Run () [0x00000] in <7a41aae9f05e45b7b5a8cedfab67f8ff>:0
  at Tomboy.GnomeApplication.StartMainLoop () [0x00001] in <f9cba0df4a314f279ace0200385e99c2>:0
  at Tomboy.Application.StartMainLoop () [0x00001] in <f9cba0df4a314f279ace0200385e99c2>:0
  at Tomboy.Tomboy.StartTrayIcon () [0x00041] in <f9cba0df4a314f279ace0200385e99c2>:0
  at Tomboy.Tomboy.Main (System.String[] args) [0x00160] in <f9cba0df4a314f279ace0200385e99c2>:0
[ERROR] FATAL UNHANDLED EXCEPTION: System.NullReferenceException: Object reference not set to an instance of an object
  at Tomboy.GnomeApplication.OnExitSignal (System.Int32 signal) [0x00001] in <f9cba0df4a314f279ace0200385e99c2>:0
  at (wrapper managed-to-native) Gtk.Application:gtk_main ()
  at Gtk.Application.Run () [0x00000] in <7a41aae9f05e45b7b5a8cedfab67f8ff>:0
  at Tomboy.GnomeApplication.StartMainLoop () [0x00001] in <f9cba0df4a314f279ace0200385e99c2>:0
  at Tomboy.Application.StartMainLoop () [0x00001] in <f9cba0df4a314f279ace0200385e99c2>:0
  at Tomboy.Tomboy.StartTrayIcon () [0x00041] in <f9cba0df4a314f279ace0200385e99c2>:0
  at Tomboy.Tomboy.Main (System.String[] args) [0x00160] in <f9cba0df4a314f279ace0200385e99c2>:0

[Johannes Rohr (jorohr)]

package version 1.15.9 on Ubuntu Bionic