self._dataset_id should have been: dataset_id
it was never assigned, therefore it had a None value, (see issue https://github.com/MicroStrategy/mstrio-py/issues/22).
To solve this, you've to pass the dataset_id to __load_definition
Thank you for your contribution @verbeemen. We have a fix for this issue coming with the next release (11.2.1) at the beginning of March 2020. Your proposal was very helpful during its development.
self._dataset_id should have been: dataset_id it was never assigned, therefore it had a None value, (see issue https://github.com/MicroStrategy/mstrio-py/issues/22). To solve this, you've to pass the dataset_id to __load_definition