Fix problems with add_swpm_fields

The released version:
1. throws an error on a new menu item
2. sets the default for a new menu item to be the membership level of not logged in
3. displays all of the membership levels in the Under navigation link.

The following code changes that:
function add_swpm_fields( $id, $item, $depth, $args ) {

//// Logged levels
$levels = $this->get_membership_levels();

$item_groups = get_post_meta( $item->ID, self::META_KEY_NAME, true );

?>
<p class=”description description-wide menu-item-actions”>
Membership groups permitted :
<?php foreach($levels as $level)
{
$key = self::META_KEY_NAME.’-‘.$level->id;
$name = sprintf( ‘%s[%s]’, $key, $item->ID );
// Handle the case where there is no array because it is a new menu item that has been added.
// In this case checkall of the member levels since it is more likely to be included than not.
if ( is_array( $item_groups ) ) {
$checked = in_array($level->id, $item_groups) || (count($item_groups) == 0 && $level->id == self::NOT_LOGGED_IN_LEVEL_ID) ? “checked” : “”;
} else {
$checked = “checked”;
}

// If the class menu-item-title is used then this is perceived to be a menu item that can be moved and will cause the
// Under link to include all of the member leves. Not good.
?>
<label class=”swpm-menu-item-title” style=”padding-top:8px;padding-bottom:8px;”>
<?php printf(
‘<input type=”checkbox” class=”menu-item-checkbox” name=”%3$s” value=”%1$s” %4$s> %2$s’,
$level->id,
$level->alias,
$name,
$checked); ?>
</label>
<?php } ?>
</p>
<?php
}

https://www.ads-software.com/plugins/simple-membership-menu/