[gnome-builder/wip/gtk4-port: 1765/1774] plugins/testui: add null precondition

[Christian Hergert <chergert src gnome org>]

commit 5779062b01bbf8558f9566fddceeb27be01ef0d1
Author: Christian Hergert <chergert redhat com>
Date:   Thu Jul 7 17:25:25 2022 -0700

    plugins/testui: add null precondition

 src/plugins/testui/gbp-testui-item.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/src/plugins/testui/gbp-testui-item.c b/src/plugins/testui/gbp-testui-item.c
index 4225f5e8d..c9e249df3 100644
--- a/src/plugins/testui/gbp-testui-item.c
+++ b/src/plugins/testui/gbp-testui-item.c
@@ -189,6 +189,7 @@ gbp_testui_item_init (GbpTestuiItem *self)
 GbpTestuiItem *
 gbp_testui_item_new (gpointer instance)
 {
+  g_return_val_if_fail (instance != NULL, NULL);
   g_return_val_if_fail (G_IS_OBJECT (instance), NULL);
 
   g_assert (IDE_IS_TEST (instance) ||