perf(invoice): Faster return amount query (#36556)

perf: Faster return amount query
(cherry picked from commit b0c79a0)

erpnext/accounts/doctype/sales_invoice/sales_invoice.py

@@ -1580,15 +1580,13 @@ def set_loyalty_program_tier(self):
 		frappe.db.set_value("Customer", self.customer, "loyalty_program_tier", lp_details.tier_name)
 
 	def get_returned_amount(self):
-		from frappe.query_builder.functions import Coalesce, Sum
+		from frappe.query_builder.functions import Sum
 
 		doc = frappe.qb.DocType(self.doctype)
 		returned_amount = (
 			frappe.qb.from_(doc)
 			.select(Sum(doc.grand_total))
-			.where(
-				(doc.docstatus == 1) & (doc.is_return == 1) & (Coalesce(doc.return_against, "") == self.name)
-			)
+			.where((doc.docstatus == 1) & (doc.is_return == 1) & (doc.return_against == self.name))
 		).run()
 
 		return abs(returned_amount[0][0]) if returned_amount[0][0] else 0