I m getting error instead of artist name

<?php

function generate_Catalog(){
       include("connection.php");
       try{
    $result = $db->query("Select media_id,title,category,img FROM media");

  }catch(Exception $e){
    echo "Unable to Retreived Result";
    echo $e->getMessage();
    exit;
  }
  $catalog = $result->fetchAll(PDO::FETCH_ASSOC);
  return $catalog;
}

function generate_single_Catalog($id){

 include("connection.php");
       try{
             $result = $db->prepare(
                        "Select title,category,img,format,genre,year,publisher,isbn 
                         FROM media
                         JOIN genres ON media.genre_id = genres.genre_id
                         LEFT OUTER JOIN books ON media.media_id = books.media_id
                         WHERE media.media_id = ?"
                         );

          $result->bindParam(1,$id,PDO::PARAM_INT);
          $result->execute();

        }catch(Exception $e){
            echo "Unable to Retreived Result";
            echo $e->getMessage();
            exit;
        }

     $item = $result->fetch(PDO::FETCH_ASSOC);

     if(empty($item)) return $item;

     try{
              $result = $db->prepare(
                    "Select fullname,role 
                     FROM media_people
                     JOIN people ON media_people.people_id = people.people_id
                     WHERE media_people.people_id = ?"
                  );

          $result->bindParam(1,$id,PDO::PARAM_INT);
          $result->execute();

    }catch(Exception $e){
              echo "Unable to Retreived Result";
              echo $e->getMessage();
              exit;
            }
  while($row = $result->fetch(PDO::FETCH_ASSOC)){
      $item[$row["role"]][] = $row["fullname"];
  }

  return $item;
}

function get_item_html($id,$item) {
    $output = "<li><a href='details.php?id="
        . $item["media_id"]. "'><img src='" 
        . $item["img"] . "' alt='" 
        . $item["title"] . "' />" 
        . "<p>View Details</p>"
        . "</a></li>";
    return $output;
}

function array_category($catalog,$category) {
    $output = array();

    foreach ($catalog as $id => $item) {
        if ($category == null OR strtolower($category) == strtolower($item["category"])) {
            $sort = $item["title"];
            $sort = ltrim($sort,"The ");
            $sort = ltrim($sort,"A ");
            $sort = ltrim($sort,"An ");
            $output[$id] = $sort;            
        }
    }

    asort($output);
    return array_keys($output);
}

<?php 
include("inc/functions.php");
$catalog = generate_Catalog();

if (isset($_GET["id"])) {
     $id = filter_input(INPUT_GET,"id",FILTER_SANITIZE_NUMBER_INT);
     $item = generate_single_Catalog($id);
     var_dump($item);
}

if (empty($item)) {
    header("location:catalog.php");
    exit;
}

$pageTitle = $item["title"];
$section = null;

include("inc/header.php"); ?>

<div class="section page">

    <div class="wrapper">

        <div class="breadcrumbs">
            <a href="catalog.php">Full Catalog</a>
            &gt; <a href="catalog.php?cat=<?php echo strtolower($item["category"]); ?>">
            <?php echo $item["category"]; ?></a>
            &gt; <?php echo $item["title"]; ?>
        </div>

        <div class="media-picture">

        <span>
            <img src="<?php echo $item["img"]; ?>" alt="<?php echo $item["title"]; ?>" />
        </span>

        </div>

        <div class="media-details">

            <h1><?php echo $item["title"]; ?></h1>
            <table>

                <tr>
                    <th>Category</th>
                    <td><?php echo $item["category"]; ?></td>
                </tr>
                <tr>
                    <th>Genre</th>
                    <td><?php echo $item["genre"]; ?></td>
                </tr>
                <tr>
                    <th>Format</th>
                    <td><?php echo $item["format"]; ?></td>
                </tr>
                <tr>
                    <th>Year</th>
                    <td><?php echo $item["year"]; ?></td>
                </tr>
                <?php if (strtolower($item["category"]) == "books") { ?>
                <tr>
                    <th>Authors</th>
                    <td><?php echo implode(", ",$item["author"]); ?></td>
                </tr>
                <tr>
                    <th>Publisher</th>
                    <td><?php echo $item["publisher"]; ?></td>
                </tr>
                <tr>
                    <th>ISBN</th>
                    <td><?php echo $item["isbn"]; ?></td>
                </tr>    
                <?php } else if (strtolower($item["category"]) == "movies") { ?>
                <tr>
                    <th>Director</th>
                    <td><?php echo implode(", ",$item["director"]); ?></td>
                </tr>
                <tr>
                    <th>Writers</th>
                    <td><?php echo implode(", ",$item["writer"]); ?></td>
                </tr>
                <tr>
                    <th>Stars</th>
                    <td><?php echo implode(", ",$item["star"]); ?></td>
                </tr>
                <?php } else if (strtolower($item["category"]) == "music") { ?>
                <tr>
                    <th>Artist</th>
                    <td><?php echo implode(", ",$item["artist"]); ?></td>
                </tr>
                <?php } ?>
            </table>

        </div>

    </div>

</div>

Notice: Undefined index: artist in C:\xampp\htdocs\pdo\pdo\details.php on line 90

Warning: implode(): Invalid arguments passed in C:\xampp\htdocs\pdo\pdo\details.php on line 90