Min max planning at org level creates a Batch without any source defined

Min max planning set at org level without any source or any sourcing rule, the item is set as Make item and replenishment with restock as Yes it creates an Batch.

However, when the Min max is set at sub inventory without any source , it gives an error

NULL Src Type.

Question:- why org level min max is not looking for any source? is is recommended to set up min max planning without any source