(gdb) bt
    #0  0x00007ffff4d9e075 in g_type_check_instance_is_fundamentally_a (type_instance=type_instance@entry=0x-1, fundamental_type=fundamental_type@entry=80) at gtype.c:4030
    #1  0x00007ffff4d7e447 in g_object_unref (_object=0xffffffffffffffff) at gobject.c:3076
    #2  0x00007fffe89cdfa8 in disconnect_context_complete (ctx=ctx@entry=0x555555b4c680) at nm-modem-broadband.c:1062
    #3  0x00007fffe89cf6e5 in disconnect (modem=<optimized out>, warn=0, cancellable=0x0, callback=0x0, user_data=0x0) at nm-modem-broadband.c:1126
    #4  0x00007fffe89d24cd in nm_modem_deactivate (self=0x555555aba1b0 [NMModemBroadband], device=device@entry=0x555555ab8c20 [NMDeviceModem]) at nm-modem.c:1164
    #5  0x00007fffdbd73022 in deactivate (device=0x555555ab8c20 [NMDeviceModem]) at nm-device-modem.c:455
    #6  0x00005555555e087b in nm_device_cleanup (self=self@entry=0x555555ab8c20 [NMDeviceModem], reason=reason@entry=NM_DEVICE_STATE_REASON_NOW_MANAGED, cleanup_type=cleanup_type@entry=CLEANUP_TYPE_DECONFIGURE)
        at devices/nm-device.c:10392
    #7  0x00005555555e0ffd in _set_state_full (self=self@entry=0x555555ab8c20 [NMDeviceModem], state=state@entry=NM_DEVICE_STATE_UNAVAILABLE, reason=reason@entry=NM_DEVICE_STATE_REASON_NOW_MANAGED, quitting=quitting@entry=0) at devices/nm-device.c:10804
    #8  0x00005555555e1a16 in nm_device_state_changed (self=self@entry=0x555555ab8c20 [NMDeviceModem], state=state@entry=NM_DEVICE_STATE_UNAVAILABLE, reason=reason@entry=NM_DEVICE_STATE_REASON_NOW_MANAGED)
        at devices/nm-device.c:11029

Fixes: 21b50c59