Index: src/wp-includes/class-wp-comment-query.php
===================================================================
--- src/wp-includes/class-wp-comment-query.php	(revision 47598)
+++ src/wp-includes/class-wp-comment-query.php	(working copy)
@@ -741,6 +741,7 @@
 
 					case 'comment':
 					case 'comments':
+						$comment_types[ $operator ][] = "''";
 						$comment_types[ $operator ][] = "'comment'";
 						break;
 
Index: src/wp-includes/comment.php
===================================================================
--- src/wp-includes/comment.php	(revision 47598)
+++ src/wp-includes/comment.php	(working copy)
@@ -1902,7 +1902,7 @@
 	$comment_karma    = ! isset( $data['comment_karma'] ) ? 0 : $data['comment_karma'];
 	$comment_approved = ! isset( $data['comment_approved'] ) ? 1 : $data['comment_approved'];
 	$comment_agent    = ! isset( $data['comment_agent'] ) ? '' : $data['comment_agent'];
-	$comment_type     = ! isset( $data['comment_type'] ) ? 'comment' : $data['comment_type'];
+	$comment_type     = empty( $data['comment_type'] ) ? 'comment' : $data['comment_type'];
 	$comment_parent   = ! isset( $data['comment_parent'] ) ? 0 : $data['comment_parent'];
 
 	$user_id = ! isset( $data['user_id'] ) ? 0 : $data['user_id'];