diff --git a/wp-comments-post.php b/wp-comments-post.php
index d6400f1519..0fc2317544 100644
--- a/wp-comments-post.php
+++ b/wp-comments-post.php
@@ -32,10 +32,10 @@ if ( empty($status->comment_status) ) {
 	exit;
 }
 
-$comment_author       = trim(strip_tags($_POST['author']));
-$comment_author_email = trim($_POST['email']);
-$comment_author_url   = trim($_POST['url']);
-$comment_content      = trim($_POST['comment']);
+$comment_author       = ( isset($_POST['author']) )  ? trim(strip_tags($_POST['author'])) : null;
+$comment_author_email = ( isset($_POST['email']) )   ? trim($_POST['email']) : null;
+$comment_author_url   = ( isset($_POST['url']) )     ? trim($_POST['url']) : null;
+$comment_content      = ( isset($_POST['comment']) ) ? trim($_POST['comment']) : null;
 
 // If the user is logged in
 $user = wp_get_current_user();
diff --git a/wp-includes/classes.php b/wp-includes/classes.php
index e6bebd5d55..0f2680118f 100644
--- a/wp-includes/classes.php
+++ b/wp-includes/classes.php
@@ -1082,8 +1082,9 @@ class Walker {
 		$id_field = $this->db_fields['id'];
 		$id = $e->$id_field;
 
-		foreach ( (array)$children_elements[$id] as $child )
-			$this->unset_children( $child, $children_elements );
+		if ( !empty($children_elements[$id]) && is_array($children_elements[$id]) )
+			foreach ( (array) $children_elements[$id] as $child )
+				$this->unset_children( $child, $children_elements );
 
 		if ( isset($children_elements[$id]) )
 			unset( $children_elements[$id] );