Memory allocating: Q_Strncpyz: NULL dest

[Exmirai]

code: 

menuDef_t *UI_CreateMenu(const char *name){
	if (menuCount < MAX_MENUS) {
		menuDef_t *menu = &Menus[menuCount];
		menu = (menuDef_t*)malloc(sizeof(menuDef_t));
		Menu_Init(menu);
		menu->itemCount = 0;
		Q_strncpyz(menu->window.name, name, sizeof(menu->window.name));
		menuCount++;
		return menu;
	}
	return NULL;
}

When I run this code, the game crashes with an error Q_Strncpyz: NULL dest, I understand the error, but can not understand exactly where I was wrong. What's the matter?

[Exmirai]

Thank to spior for solving my problem