Is it mandatory to sort,partition for JOIN

[ds_is_fun]

I did not use sort, hash partition by key columns on the join. Rather left to default auto and ran. There were some data columns that came in with a blank values on the left join. I then changed it to sort,partition and data columns came in right without any blank values. I checked my data for testing this and there was no way blanks should have come in the first step.
Is it mandatory to sort, partition for a join stage?
Thanks

[ray.wurlod]

Yes. Several stage types, Join among them, are documented as requiring that their inputs be sorted.