fix: the empty object being passed for the wp_query object

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

@@ -3662,14 +3662,24 @@ private function set_found_posts( $q, $limits ) {
 	 *
 	 * @since 1.5.0
 	 *
-	 * @return WP_Post Next post.
+	 * @return WP_Post|int Next post.
 	 */
 	public function next_post() {
 
 		++$this->current_post;
 
-		/** @var WP_Post */
-		$this->post = $this->posts[ $this->current_post ];
+		if ( $this->posts[ $this->current_post ] instanceof WP_Post ) {
+			$this->post = $this->posts[ $this->current_post ];
+		} else {
+			$current_item = $this->posts[ $this->current_post ];
+
+			if ( is_object( $current_item ) && property_exists( $current_item, 'ID' ) ) {
+				$this->post = $current_item->ID;
+			} else {
+				$this->post = $current_item;
+			}
+		}
+
 		return $this->post;
 	}