This app crashes when not modifying the keyboard shortcuts to be invalid.

keyboard-accelerator.c

#include <gtk-4.0/gtk/gtk.h>

static void
handler (void)
{
  printf("Hello, world!");
}

static void
activate (GtkApplication *app,
          gpointer        user_data)
{
  GtkWidget *window;

  window = gtk_application_window_new (app);
  gtk_window_set_title (GTK_WINDOW (window), "Hello GNOME");
  gtk_window_present (GTK_WINDOW (window));

  const char *action_id = "action";
  GSimpleAction *action = g_simple_action_new (action_id, NULL);
  g_action_map_add_action (G_ACTION_MAP (app), G_ACTION (action));
  g_signal_connect (action, "activate", G_CALLBACK (handler), NULL);
  // Remove "Ctrl" ({ "<>n" })
  // or add an invalid shortcut ({ "<Ctrl>n", "<>f" })
  // and the app doesn't crash.
  // 
  // SOLUTION: Add NULL to the end ({ "<Ctrl>n", NULL })
  const char *keyboard_shortcuts[] = { "<Ctrl>n" };
  const char *full_id = "app.action";
  gtk_application_set_accels_for_action (GTK_APPLICATION (app), full_id, keyboard_shortcuts);
}

int
main (int   argc,
      char *argv[])
{
  GtkApplication *app = gtk_application_new ("test.test.TestyTest", G_APPLICATION_DEFAULT_FLAGS);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
  int status = g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);
  return status;
}