Ticket #39428: 39428.2.diff

src/wp-includes/class-wp-query.php

@@ -2431 +2431 @@
                         $q['author']      = get_user_by( 'slug', $q['author_name'] );
                         if ( $q['author'] ) {
                                 $q['author'] = $q['author']->ID;
+                        } else {
+                                return array();
                         }
                         $whichauthor .= " AND ({$wpdb->posts}.post_author = " . absint( $q['author'] ) . ')';
                 }