Co-authors plus guest authors do not display

[timburden]

Passing authors to a twig file from get_coauthors() works fine unless the authors are guest authors.

Expected behavior

Guest authors would display properly using author.name and author.link

Actual behavior

These values are null

Steps to reproduce behavior

In a template file:

require_once( dirname( __FILE__ ) . '/includes/class-sjmpost.php' );
$mposts = Timber::get_posts( $args, 'SJMPost' );

class-sjmpost.php

class SJMPost extends TimberPost {

    /**
     * Provides an authors method to twig, which conditionally uses Co-Authors Plus if available.
     */
    function authors() {
        $authors = array();
        if ( function_exists( 'get_coauthors' ) ) {

            $cauthors = get_coauthors( $this->ID );
            foreach ( $cauthors as $author ) {
                    $author = new Timber\User( $author );
                    var_dump( $author );
                    $authors[] = $author;
            }
        } else {
            $authors[] = new Timber\User( $this->post_author );
        }

        return $authors;
    }
}

In twig file:

{{ post.authors | wrap_and_join('<a href="{{item.link}}">{{item.name}}</a>', ' and ' ) }}

wrap_and_join() is just a twig extension for joining arrays of objects with a twig snippet.
At the var_dump( $author ), the user object is filled out properly if the author is a real user, but not if it is a co-authors plus guest author. he following shows partial output from one real user and one guest user:

// real user
object(Timber\User)#1843 (46) {
--
  | ["object_type"]=>
  | string(4) "user"
  | ["_link"]=>
  | NULL
  | ["description"]=>
  | string(0) ""
  | ["display_name"]=>
  | string(16) "Malcolm Johnston"

//guest user

object(Timber\User)#1841 (11) {
--
  | ["object_type"]=>
  | string(4) "user"
  | ["_link"]=>
  | NULL
  | ["description"]=>
  | NULL
  | ["display_name"]=>
  | NULL

What version of WordPress, PHP and Timber are you using?

WP 4.8.1, PHP 7.0.23, Timber 1.5.2

How did you install Timber? (for example, from GitHub, Composer/Packagist, WP.org?)

Download from WP.org

[timburden]

My code is based on the snippets provided in this issue: #1158

[Levdbas]

Usage of external plugin and stale for a while, closing.