I'm using ADX, it appears that Table.FirstN(..., 0) does not fold. It appears that there is an optimization that returns a black table when this happens, but this table is not a view and as such folding fails.
Test case (make sure direct query is on):
Table.FirstN(AzureDataExplorer.Contents("help", "Samples", "print 0"), 0)
The help server is configured to let everyone use it.
I have submitted this to PG, ICM:210162261
will update here once I get any information.