Issues with tutorials in Stardog Studio

recently I started experimenting with Stardog Studio.
I really liked how the tutorial creates new databases, so one can get started right away.
Yet, in my setup the default namespaces used in the tutorial and the default namespaces of the newly created DBs did not match.
Which is easy to fix, but I just wanted to point it out to you.

Also I ran in another issue. I cannot pin point if it is my mistake or a bug, but when doing the exercises (SPARQL 103: Additional Operations), I ran into a Nullpointer Exception.

com.complexible.stardog.plan.eval.operator.OperatorException: Uncaught error during query evaluation: NullPointerException:

This was caused by running this query:

SELECT ?year ?count 
        SELECT ?year (COUNT(?album) AS ?count)
            ?album a :Album ;
                :date ?date .
            BIND(YEAR(?date) as ?year)
        GROUP BY ?year
    FILTER(avg(?count) < ?count)
ORDER BY ?count

However, if the calculated average is replaced with a previously calculated value (18.55) it works just fine. Is it not possible to calculate the average on the fly? Or did I really ran into some kind of bug?