fix: item price query for postgres

postgres doesn't like bad type comparisons and doesn't have `isnull`
funciton

erpnext/stock/doctype/item_price/item_price.py

@@ -5,6 +5,8 @@
 import frappe
 from frappe import _
 from frappe.model.document import Document
+from frappe.query_builder import Criterion
+from frappe.query_builder.functions import Cast_
 from frappe.utils import getdate
 
 
@@ -48,35 +50,57 @@ class ItemPrice(Document):
 			)
 
 	def check_duplicates(self):
-		conditions = (
-			"""where item_code = %(item_code)s and price_list = %(price_list)s and name != %(name)s"""
-		)
 
-		for field in [
+		item_price = frappe.qb.DocType("Item Price")
+
+		query = (
+			frappe.qb.from_(item_price)
+			.select(item_price.price_list_rate)
+			.where(
+				(item_price.item_code == self.item_code)
+				& (item_price.price_list == self.price_list)
+				& (item_price.name != self.name)
+			)
+		)
+		data_fields = (
 			"uom",
 			"valid_from",
 			"valid_upto",
-			"packing_unit",
 			"customer",
 			"supplier",
 			"batch_no",
-		]:
-			if self.get(field):
-				conditions += " and {0} = %({0})s ".format(field)
-			else:
-				conditions += "and ({0} is null or {0} = '')".format(field)
-
-		price_list_rate = frappe.db.sql(
-			"""
-				select price_list_rate
-				from `tabItem Price`
-				{conditions}
-			""".format(
-				conditions=conditions
-			),
-			self.as_dict(),
 		)
 
+		number_fields = ["packing_unit"]
+
+		for field in data_fields:
+			if self.get(field):
+				query = query.where(item_price[field] == self.get(field))
+			else:
+				query = query.where(
+					Criterion.any(
+						[
+							item_price[field].isnull(),
+							Cast_(item_price[field], "varchar") == "",
+						]
+					)
+				)
+
+		for field in number_fields:
+			if self.get(field):
+				query = query.where(item_price[field] == self.get(field))
+			else:
+				query = query.where(
+					Criterion.any(
+						[
+							item_price[field].isnull(),
+							item_price[field] == 0,
+						]
+					)
+				)
+
+		price_list_rate = query.run(as_dict=True)
+
 		if price_list_rate:
 			frappe.throw(
 				_(