Aggregating SPARQL query doesn't work anymore

[mvanbrab]

Description
A previously working query using AVG and GROUP BY no longer works.
It gives an error saying "part.triples not iterable".

Versions
Was working in version ref2-internal.
Found not working in versions v1.0.0 and v1.1.0.

Input files
The configuration file (copy into src directory):
config.json

The query file (copy into public/queries directory and change file extension from .txt to .rq):
manufacturer-average-recycled-content-of-products.txt

References
See this online deployed version (still using version ref2-internal at the time of writing):
https://viewer.onto-deside.ilabt.imec.be/