diff -r 3d4e9c994f10 -r a86126ab1dd4 wp/wp-includes/class-wp-comment.php
--- a/wp/wp-includes/class-wp-comment.php	Tue Oct 22 16:11:46 2019 +0200
+++ b/wp/wp-includes/class-wp-comment.php	Tue Dec 15 13:49:49 2020 +0100
@@ -114,9 +114,10 @@
 	 * Comment type.
 	 *
 	 * @since 4.4.0
+	 * @since 5.5.0 Default value changed to `comment`.
 	 * @var string
 	 */
-	public $comment_type = '';
+	public $comment_type = 'comment';
 
 	/**
 	 * Parent comment ID.
@@ -251,7 +252,7 @@
 	 *                                 `$meta_query`. Also accepts false, an empty array, or
 	 *                                 'none' to disable `ORDER BY` clause.
 	 * }
-	 * @return array Array of `WP_Comment` objects.
+	 * @return WP_Comment[] Array of `WP_Comment` objects.
 	 */
 	public function get_children( $args = array() ) {
 		$defaults = array(
@@ -343,7 +344,7 @@
 	 * @return bool
 	 */
 	public function __isset( $name ) {
-		if ( in_array( $name, $this->post_fields ) && 0 !== (int) $this->comment_post_ID ) {
+		if ( in_array( $name, $this->post_fields, true ) && 0 !== (int) $this->comment_post_ID ) {
 			$post = get_post( $this->comment_post_ID );
 			return property_exists( $post, $name );
 		}
@@ -360,7 +361,7 @@
 	 * @return mixed
 	 */
 	public function __get( $name ) {
-		if ( in_array( $name, $this->post_fields ) ) {
+		if ( in_array( $name, $this->post_fields, true ) ) {
 			$post = get_post( $this->comment_post_ID );
 			return $post->$name;
 		}