Wordpress: How do I resolve Notice: Undefined offset: 0 in /wp-includes/capabilities.php on line 1145 - undefined

Question

I've looked at previous examples of this problem but I can't find a solution for what is causing this notice based on what I've seen from other people. This appears when I am adding a new post only.
1145 is:
$post = get_post( $args[0] );
I'm not getting any other kind of error so I'm not sure where in my code this is causing the problem.
Any help on this?
This is the code:
//show metabox in post editing page
add_action('add_meta_boxes', 'kk_add_metabox' );
//save metabox data
add_action('save_post', 'kk_save_metabox' );
//register widgets
add_action('widgets_init', 'kk_widget_init');
function kk_add_metabox() {
add_meta_box('kk_youtube', 'YouTube Video Link','kk_youtube_handler', 'post');
}
/**
* metabox handler
*/
function kk_youtube_handler($post)
{
$youtube_link = esc_attr( get_post_meta( $post->ID, 'kk_youtube', true ) );
echo '<label for="kk_youtube">YouTube Video Link</label><input type="text" id="kk_youtube" name="kk_youtube" value="' . $youtube_link . '" />';
}
/**
* save metadata
*/
function kk_save_metabox($post_id) {
if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
return;
}
//check if user can edit post
if( !current_user_can( 'edit_post' ) ) {
return;
}
if( isset($_POST['kk_youtube'] )) {
update_post_meta($post_id, 'kk_youtube', esc_url($_POST['kk_youtube']));
}
}
/**
* register widget
*/
function kk_widget_init() {
register_widget('KK_Widget');
}
/**
* Class KK_Widget widget class
*/
class KK_Widget extends WP_Widget
{
function __construct()
{
$widget_options = array(
'classname' => 'kk_class', // For CSS class name
'description' => 'Show a YouTube video from post metadata'
);
$this->WP_Widget('kk_id', 'YouTube Video', $widget_options);
}
/**
* Show widget form in Appearance/Widgets
*/
function form($instance)
{
$defaults = array(
'title' => 'YouTube Video'
);
$instance = wp_parse_args((array)$instance, $defaults);
var_dump($instance);
$title = esc_attr($instance['title']);
echo '<p>Title <input type="text" class="widefat" name="' . $this->get_field_name('title') . '" value="' . $title . '" /></p>';
}
function update($new_instance, $old_instance)
{
$instance = $old_instance;
$instance['title'] = strip_tags($new_instance['title']);
return $instance;
}
/**
* Show widget in post/page
*/
function widget($args, $instance)
{
global $before_widget;
global $after_widget;
global $before_title;
global $after_title;
extract( $args );
$title = apply_filters('widget_title', $instance['title']);
//show only if single post
if(is_single()) {
echo $before_widget;
echo $before_title.$title.$after_title;
//get post metadata
$kk_youtube = esc_url(get_post_meta(get_the_ID(), 'kk_youtube', true));
//print widget content
echo '<iframe width="200" height="200" frameborder="0" allowfullscreen src="http://www.youtube.com/embed/' . $this->get_yt_videoid($kk_youtube) . '"></iframe>';
echo $after_widget;
}
}
function get_yt_videoid($url)
{
parse_str(parse_url($url, PHP_URL_QUERY), $my_array_of_vars);
return $my_array_of_vars['v'];
}
}

Answer 1

I found the solution here https://wordpress.org/support/topic/patch-notice-undefined-offset-0-in-capabilitiesphp-on-line-1102
May seem different issue but I could fix the issue changing:
if ( ! current_user_can( 'edit_post' ) ) return;
to
if ( ! current_user_can( 'edit_posts' ) ) return;
In other scenary
if you have a custom taxonomy, you must be sure that 'assign_term' capability on 'capabilities' args is related to 'edit_posts'
'assign_terms' => 'edit_posts',
or
'assign_terms' => 'edit_mycustomposttypes',
(note the 's' at end)
example:
$capabilities = array(
'manage_terms' => 'manage_mytaxs',
'edit_terms' => 'manage_mytaxs',
'delete_terms' => 'manage_mytaxs',
**'assign_terms' => 'edit_mycustomposttypes',**
);
$args = array(
'show_ui' => true,
'show_admin_column' => true,
**'capabilities' => $capabilities,**
);
register_taxonomy( 'mytax', 'mycustomposttype', $args );

Answer 2

This line:
if( !current_user_can( 'edit_post' ) ) {
Should be:
if( !current_user_can( 'edit_post', $post_id ) ) {