Description of problem:
Added an entry, and it crashed.

The entry was added- I can see it now when I've restarted the application

Version-Release number of selected component:
gnome-calendar-3.28.1-1.fc28

Additional info:
reporter:       libreport-2.9.4
backtrace_rating: 4
cmdline:        /usr/bin/gnome-calendar --gapplication-service
crash_function: GCAL_IS_MANAGER
executable:     /usr/bin/gnome-calendar
journald_cursor: s=14326aefa44342edb1e41e545a13dfd1;i=503f22;b=b2ca8a461ec446a48998ad114f8e702f;m=28d543e67a;t=56a351ae5c0cc;x=75070c52f4fd6a22
kernel:         4.16.1-300.fc28.x86_64
rootdir:        /
runlevel:       N 5
type:           CCpp
uid:            1000

Truncated backtrace:
Thread no. 1 (10 frames)
 #0 GCAL_IS_MANAGER at ../src/gcal-manager.h:33
 #1 gcal_manager_get_default_source at ../src/gcal-manager.c:1081
 #2 update_default_calendar_row at ../src/gcal-quick-add-popover.c:487
 #8 g_object_notify_queue_thaw at gobject.c:296
 #9 g_object_setv at gobject.c:2250
 #10 g_object_set_property at gobject.c:2531
 #11 on_source_notify at gbinding.c:327
 #17 g_object_notify_by_spec_internal at gobject.c:1175
 #23 g_settings_real_change_event at gsettings.c:386
 #24 ffi_call_unix64 at ../src/x86/unix64.S:76

Potential duplicate: bug 1544538