I am developing custom theme from scratch and creates a custom post type and getting this warning while editing custom post type. I also design custom Meta box with two input fields and using nonce in it. Any help removing these warning?

Here is code of custom metabox in functions.php

//Custom Metabox

function register_book_meta_box(){
    add_meta_box('book_meta_box_id', 'Book Detail','design_book_meta_box','books','advanced','high');
}
add_action('add_meta_boxes','register_book_meta_box');

function design_book_meta_box($post){
    wp_nonce_field(basename(__FILE__),'book_cpt_nonce')
    ?>
        <div>
            <label for="book-author">Author Name&nbsp;&nbsp;</label>
            <input type="text" name="book-author" placeholder="Author Name" value="<?php echo get_post_meta( $post->ID, 'book-author-key', true );?>">
        </div>
        <div>
            <label for="year">Published Year</label>
            <input type="number" id="year" name="year" min="1455" max="2020" value="<?php echo get_post_meta( $post->ID, 'book-year-key', true );?>">
            <span id="errorMsg" style="display:none;">Published Year Must be range from 1455 - 2020</span>
        </div>

    <?php
}
function save_book_meta_data($post_id)
{
    if(!isset($_POST['book_cpt_nonce']) || !wp_verify_nonce($_POST['book_cpt_nonce'],basename(__FILE__))){
        return $post_id;
    }
    if (array_key_exists('book-author', $_POST)) {
        update_post_meta( $post_id,'book-author-key', $_POST['book-author']
        );
    }
    if (array_key_exists('year', $_POST)) {
        update_post_meta( $post_id,'book-year-key', $_POST['year']
        );
    }
}
add_action('save_post', 'save_book_meta_data');

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