GSettings delayed apply generates runtime warnings

This is with glib2-2.68.1.

I tried delayed apply and it generates runtime warnings:

(process:37736): GLib-CRITICAL **: 10:23:18.095: g_variant_ref: assertion 'value != NULL' failed
	   at g_logv() at gmessages.c:1331
	   by g_log() at gmessages.c:1490
	   by g_return_if_fail_warning() at gmessages.c:2962
	   by g_variant_ref() at gvariant-core.c:733
	   by add_to_tree() at gdelayedsettingsbackend.c:159
	   by g_tree_foreach() at gtree.c:1121
	   by g_delayed_settings_backend_write_tree() at gdelayedsettingsbackend.c:175
	   by g_settings_backend_write_tree() at gsettingsbackend.c:837
	   by g_delayed_settings_backend_apply() at gdelayedsettingsbackend.c:261
	   by g_settings_apply() at gsettings.c:2298

I did call also g_settings_reset, before calling g_settings_apply(), if it matters.