Non-working GDBus BlueZ thing

bztest.c

//gcc -Wall bztest.c $(pkg-config --cflags --libs gio-2.0)
#include <stdlib.h>
#include <gio/gio.h>

#define NOPE(obj) \
G_STMT_START \
if (!obj) \
{ \
	retval = EXIT_FAILURE; \
	goto exit; \
} \
G_STMT_END

int main (void) {
	int retval = EXIT_SUCCESS;

	g_type_init();

	GDBusConnection *sys = g_bus_get_sync(G_BUS_TYPE_SYSTEM, NULL, NULL);
	NOPE(sys);
	GVariant *adapter_tuple = g_dbus_connection_call_sync(sys,
								"org.bluez", 
								"/",
								"org.bluez.Manager", 
								"DefaultAdapter",
								NULL, 
								((const GVariantType *) "(o)"),
								G_DBUS_CALL_FLAGS_NONE,
								-1,
								NULL,
								NULL);
	NOPE(adapter_tuple);
	GVariant *adapter = g_variant_get_child_value(adapter_tuple, 0);
	NOPE(adapter);

	GVariant *adapter_properties_tuple = g_dbus_connection_call_sync(sys,
									  "org.bluez", 
									  g_variant_get_string(adapter, NULL),
									  "org.bluez.Adapter", 
									  "GetProperties",
									  NULL, 
									  ((const GVariantType *) "(a{sv})"),
									  G_DBUS_CALL_FLAGS_NONE,
									  -1,
									  NULL,
									  NULL);
	NOPE(adapter_properties_tuple);
	GVariant *adapter_properties = g_variant_get_child_value(adapter_properties_tuple, 0);
	NOPE(adapter_properties);
	GVariant *registered_devices = g_variant_lookup_value(adapter_properties, "Devices", G_VARIANT_TYPE_OBJECT_PATH_ARRAY);
	NOPE(registered_devices);
	gsize children = g_variant_n_children(registered_devices);
	if (children > 0)
	{
		int i;
		for (i = 0; i != children; ++i)
		{
			GVariant *dev = g_variant_get_child_value(registered_devices, i);
			if (g_variant_is_of_type (dev, G_VARIANT_TYPE_OBJECT_PATH))
			{
				(void) g_dbus_connection_call_sync(sys,
								    "org.bluez", 
								    g_variant_get_string(dev, NULL), 
								    "org.bluez.Device", 
								    "Disconnect", 
								    NULL, 
								    NULL, 
								    G_DBUS_CALL_FLAGS_NONE,
								    -1,
								    NULL,
								    NULL);
			}
			g_variant_unref(dev);
		}
	}

	(void) g_dbus_connection_call_sync(sys,
					    "org.bluez", 
					    g_variant_get_string(adapter, NULL), 
					    "org.bluez.Adapter", 
					    "SetProperty", 
					     g_variant_new("sv", "Powered", g_variant_new_variant(g_variant_new_boolean(FALSE))), //Possible leak: Check if g_variant_new_variant's floating reference is taken by g_variant_new
					     NULL, 
					     G_DBUS_CALL_FLAGS_NONE,
					     -1,
					     NULL,
					     NULL);

exit:
	if (registered_devices)
		g_variant_unref(registered_devices);
	if (adapter_properties)
		g_variant_unref(adapter_properties);
	if (adapter_properties_tuple)
		g_variant_unref(adapter_properties_tuple);
	if (adapter)
		g_variant_unref(adapter);
	if (adapter_tuple)
		g_variant_unref(adapter_tuple);
	if (sys)
		g_object_unref (sys);
	return retval;
}