Power BI Non-null assertion failure

Thanks for parry2k's concern about this issue. 

Hi, mdw 

I am glad to help you.

May I ask what type of data source are you using? What operation is being performed that is causing this error? Is a very large dataset being used?

In Power BI, this error may occur if the dataset is too large or the query is complex such that the memory consumed by the query or calculation exceeds the configured limit.

If this is the reason, you can try to optimize your dataset by simplifying the query and removing unnecessary columns to reduce memory consumption.
If you are using import mode to connect to the data source, you may also want to consider using DirectQuery mode or Live Connection mode to connect to the data source.

I hope my suggestions give you good ideas, if you have any more questions, please clarify in a follow-up reply.
Best Regards,
Fen Ling,
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