AutoAggs: Object Reference not set to an instance

[ruhrpotter]

When running the script this error comes up at line 25:

When outputting p.Query it returns Null. p is correctly set to the first partition of the fact table.

The way I understand it, it tries to find the query for a partition, but it's empty? I've already setup incremental refresh on the fact table, whch is why the partitions themselves do not have it's own M query. It's in the "SourceExpression" attribute of the table object. Is this why it fails?