diff -uNr xfce4-session-4.13.1.orig/xfce4-session/xfsm-fadeout.c xfce4-session-4.13.1/xfce4-session/xfsm-fadeout.c
--- xfce4-session-4.13.1.orig/xfce4-session/xfsm-fadeout.c	2017-12-07 08:01:16.000000000 +0100
+++ xfce4-session-4.13.1/xfce4-session/xfsm-fadeout.c	2019-01-01 14:14:43.946292896 +0100
@@ -157,6 +157,7 @@
   for (n = 0; n < XScreenCount (fadeout->xdisplay); ++n)
     {
       screen = gdk_display_get_screen (display, n);
+      if (screen == NULL) continue;
       xwindow = xfsm_x11_fadeout_new_window (display, screen);
       fadeout->xwindows = g_slist_prepend (fadeout->xwindows, GINT_TO_POINTER (xwindow));
     }
Binary files xfce4-session-4.13.1.orig/xfce4-session/.xfsm-fadeout.c.swp and xfce4-session-4.13.1/xfce4-session/.xfsm-fadeout.c.swp differ