Undefined index on cURL request on Graph API

Question

I'm using Facebook's graph API to retrieve some data via a cURL call in PHP and I'm receiving an Undefined index error and I don't know how to target it correctly.

cURL Request:

<?php
/* Call the cURL request to pull in Instagram images */
$curl = curl_init();
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_URL, "https://graph.facebook.com/v5.0/". get_option('insta_id') ."/media?fields=media_url,permalink,username,media_type,thumbnail_url&access_token=". get_option('insta_accesstoken'));
$result = curl_exec($curl);
$array = json_decode($result, true);
?>

Array mapping:

<?php
/* Loop through the array and only pull API fields */
$mediaUrls = array_map(function($entry) {
    return [
        'media_url' => $entry['media_url'],
        'permalink' => $entry['permalink'],
        'username' => $entry['username'],
        'media_type' => $entry['media_type'],
        'thumbnail_url' => $entry['thumbnail_url']
    ];
}, $array['data']);
?>

Via the Graph API, some have the thumbnail_url and some don't as shown below:

I am receiving an debug error as below:

Answer 1

Correct answer was 'thumbnail_url' => !empty($entry['thumbnail_url']) ? $entry['thumbnail_url'] : "" by @CD001.