node to traverse cannot be null (Hibernate SQL)

I'm performing a SQL query through hibernate, which looks like:

SELECT thi 
FROM track_history_items thi 
JOIN artists art 
  ON thi.artist_id = art.id 
WHERE thi.type = "TrackBroadcast" 
GROUP BY art.name 
ORDER thi.createdAt DESC

but I'm getting the message that 'Node to traverse cannot be null!'. Anyone know what could be causing this?

--EDIT--

I'm pretty sure that this problem is being caused by the possibility of artist_id to be null. However, I can't prevent this, so can I just skip the rows track_history_item rows which have a null artist_id?