A workaround which will allow to not define ‘dummy’ ‘Add New’ submenu items is to add to the user role ‘create_posts’, ‘edit_posts’ capability. It’s possible to block that menu with URE Pro “Admin menu access” add-on.

In other cases WordPress requires that there was a correspondent menu item available for current user if he tries to access ‘post-new.php’ page.

You can find logic at user_can_access_admin_page() function.
It’s located at wp-admin/includes/plugin.php file, line # 1697.
It’s called from wp-admin/includes/menu.php file, line # 333.