How to customise RequisitionLinePartList to add a new attribute?

Hi,

There is a requirement to add a new attribute to Purchase Requisition| Part Requisition Lines tab. To do that, new attribute to be added to below list.

RequisitionLinePartList is derived from fragment PurchaseReqLinePartTab. But it is a clone of RequisitionLinePartBaseList.

RequisitionLinePartBaseList is created from PurchaseReqLinePart entity as below.

I have overridden entity PurchaseReqLinePart in PurchaseRequisitionHandling-Cust.projection to add new attribute.

But to add this to RequisitionLinePartList, I wrote the below code in PurchaseRequisition-cust.client file but it gives me below error.

How can I fix this? 

Appreciate comments. 

Thank you.