I just found that under special circumstances 
	system_default = g_tls_backend_get_default_database (g_tls_backend_get_default ());
may return NULL.
I added a 
	if(system_default) 
on line 476
----------------------------------
static void
set_use_system_ca_file (SoupSession *session, gboolean use_system_ca_file)
{
	SoupSessionPrivate *priv = SOUP_SESSION_GET_PRIVATE (session);
	GTlsDatabase *system_default;

	system_default = g_tls_backend_get_default_database (g_tls_backend_get_default ());

	if (use_system_ca_file)
		set_tlsdb (session, system_default);
	else if (priv->tlsdb == system_default)
		set_tlsdb (session, NULL);

	if(system_default) 
		g_object_unref (system_default);
}