add_filter priority problem

1. The get_avatar filter accepts 6 parameters, not 5.

2. The $id_or_email can also be an instance of WP_Post, WP_User or a md5 hash string. So it’s better to extract $user_id like this:

 if ( is_numeric( $id_or_email ) ) {
     $user_id = $id_or_email;
 } elseif ( is_string($id_or_email) ) {
     if ( is_email($id_or_email) ) {
         $user = get_user_by('email', $id_or_email);
         $user_id = $user->ID;
     } else { // md5 hash string
         // Do something.
     }
 } elseif ( is_object($id_or_email) ) {
     if ($id_or_email instanceof \WP_User) {
         $user_id = $id_or_email->ID;
     } elseif ($id_or_email instanceof \WP_Post) {
         $user_id = $id_or_email->post_author;
     } else {
         $user_id = $id_or_email->user_id;
     }
 } else {
     return $avatar;
 } 

3. Make sure the get_user_meta( $user_id, 'basic_user_avatar', true ) return something. If nothing is returned, default $avatar will be used.