chore: Fix a potential variable misuse bug (#31372)

* Fix a potential variable misuse bug

* chore: Separate check (separate line) for empty table in Pricing Rule

* chore: Code readability & check for field in row (now row itself)

Co-authored-by: marination <maricadsouza221197@gmail.com>

erpnext/accounts/doctype/pricing_rule/pricing_rule.py

@@ -36,8 +36,12 @@ def validate(self):
 
 	def validate_duplicate_apply_on(self):
 		if self.apply_on != "Transaction":
-			field = apply_on_dict.get(self.apply_on)
-			values = [d.get(frappe.scrub(self.apply_on)) for d in self.get(field) if field]
+			apply_on_table = apply_on_dict.get(self.apply_on)
+			if not apply_on_table:
+				return
+
+			apply_on_field = frappe.scrub(self.apply_on)
+			values = [d.get(apply_on_field) for d in self.get(apply_on_table) if d.get(apply_on_field)]
 			if len(values) != len(set(values)):
 				frappe.throw(_("Duplicate {0} found in the table").format(self.apply_on))