WORPDRESS AUTHOR IMAGE PHP

 <div class="author-image"><?php
$get_author_id = get_the_author_meta('ID');
$get_author_gravatar = get_avatar_url($get_author_id, array('size' => 300));
if(has_post_thumbnail()){
    the_post_thumbnail();
} else {
    echo '<img src="'.$get_author_gravatar.'" alt="'.get_the_title().'" />';
}
?></div>