Getting transient Null Exception when refreshing a data source

[RezaAssadi]

I keep getting the error below when I do a full refresh on my Power BI report. However, refreshing the data source individually works without any issue. 

OLE DB or ODBC error: [Expression.Error] We cannot apply field access to the type Null.

How come the refresh only fails when I refresh all data sources across the report? And how can I see what the offending column is?

[RezaAssadi]

I was ultimately unable to figure out the root cause of the issue and ended up rewriting a bunch of queries to make this work. The fact that PowerBI fails due to a null exception but never tells you what that null exception is feels really broken. 

[vojtechsima]

@RezaAssadi hello,

do you have some dependency on some tables, or are you waiting for some query to finish before you get values for another one, that's the only thing I can think of.

[RezaAssadi]

I do have different references between different tables. However, that used to work just fine before and I am not entirely sure why it would only break if I refresh all Data Sources at once (and not when I just refresh this one data source). What's more challenging is that there are no error logs telling me which column has a null reference and where that null reference is. I verified the underlying query and confirmed none of the columns are null.