Extension method: Modifier "this" is not valid for this item

[NIA]

    public static class GameObjectUtils {
        public static string GetFullPath(this Transform transform) {
            string path = transform.name;
            while (transform.parent != null) {
                transform = transform.parent;
                path = transform.name + "/" + path;
            }
            return path;
        }
    }

This happens on every extension method in every static class, both in my Unity and plain C# projects.

[VISTALL]

Hello. Fixed. It's my mistake (i added this modifier to generic parameter not parameter :D)

Thanks