Comment 2 for bug 1728172

StacktraceTop:
 g_type_check_instance_cast (type_instance=0x556f547c8790, iface_type=93936654741120) at ../../../../gobject/gtype.c:4057
 ext_ubuntu_dock_placement_changed_callback (settings=<optimized out>, key=<optimized out>, user_data=<optimized out>) at cc-ubuntu-panel.c:258
 g_closure_invoke (closure=0x556f54703100, return_value=0x0, n_param_values=2, param_values=0x7ffd9dcc9c60, invocation_hint=0x7ffd9dcc9be0) at ../../../../gobject/gclosure.c:804
 signal_emit_unlocked_R (node=node@entry=0x556f53f95a00, detail=detail@entry=4427, instance=instance@entry=0x556f544e7700, emission_return=emission_return@entry=0x0, instance_and_params=instance_and_params@entry=0x7ffd9dcc9c60) at ../../../../gobject/gsignal.c:3635
 g_signal_emit_valist (instance=0x556f544e7700, signal_id=<optimized out>, detail=4427, var_args=var_args@entry=0x7ffd9dcc9e30) at ../../../../gobject/gsignal.c:3391