How can I filter by property type

Some time ago, we discovered that a certain timestamp property was being stored as a String instead of a Long in our database. This issue is now fixed, but some of the old data is still hanging around and I want to filter it out of a query that I'm writing. How can I exclude all the vertices that contain the property with type String? I tried using a lambda but I think they are disallowed and always return errors in Neptune.