fix: 'NoneType' object is not iterable (#39977)

diff --git a/erpnext/stock/doctype/pick_list/pick_list.py b/erpnext/stock/doctype/pick_list/pick_list.py
index 0e1f8d7..8a1f79d 100644
--- a/erpnext/stock/doctype/pick_list/pick_list.py
+++ b/erpnext/stock/doctype/pick_list/pick_list.py
@@ -73,6 +73,10 @@
 		self.update_status()
 		self.set_item_locations()
 
+		if self.get("locations"):
+			self.validate_sales_order_percentage()
+
+	def validate_sales_order_percentage(self):
 		# set percentage picked in SO
 		for location in self.get("locations"):
 			if (