Wordpress - Custom meta box with checkbox field

functions.php

function slider_get_meta( $value ) {
 global $post;

 $field = get_post_meta( $post->ID, $value, true );
 if ( ! empty( $field ) ) {
   return is_array( $field ) ? stripslashes_deep( $field ) : stripslashes( wp_kses_decode_entities( $field ) );
 } else {
   return false;
 }
}
//creating meta box
function slider_add_meta_box() {
  add_meta_box(
    'memory_meta', //id
    __( 'Əlavə sahələr', 'custom_meta_fields' ), //title
    'slider_html', // callback
    '', // screen - The screen or screens on which to show the box (such as a post type, 'link', or 'comment').
    'normal', // context -  The context within the screen where the boxes should display.
    'default' //   priority - The priority within the context where the boxes should show ('high', 'low').
  );
}
add_action( 'add_meta_boxes', 'slider_add_meta_box' );

//callback function
function slider_html( $post) {
  wp_nonce_field( '_slider_nonce', 'slider_nonce' ); ?>

  <p>
    
    <input type="checkbox" name="slider" id="slider" value="yes" <?php echo slider_get_meta( 'slider' ) == 'yes'? 'checked':''; ?>> 
    <label for="slider"><?php _e( 'Display on slider', 'slider' ); ?></label>

  </p>

  <?php
}

// saving
function slider_save( $post_id ) {
  if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return;
  if ( ! isset( $_POST['slider_nonce'] ) || ! wp_verify_nonce( $_POST['slider_nonce'], '_slider_nonce' ) ) return;
  if ( ! current_user_can( 'edit_post', $post_id ) ) return;

  
    update_post_meta( $post_id, 'slider',  $_POST['slider']  );

}
add_action( 'save_post', 'slider_save' );