fix: handle None case for get_shipping_amount_from_rules (#19723)

diff --git a/erpnext/accounts/doctype/shipping_rule/shipping_rule.py b/erpnext/accounts/doctype/shipping_rule/shipping_rule.py
index a20f5c0..8c4efbe 100644
--- a/erpnext/accounts/doctype/shipping_rule/shipping_rule.py
+++ b/erpnext/accounts/doctype/shipping_rule/shipping_rule.py
@@ -70,7 +70,7 @@
 
 	def get_shipping_amount_from_rules(self, value):
 		for condition in self.get("conditions"):
-			if not condition.to_value or (flt(condition.from_value) <= value <= flt(condition.to_value)):
+			if not condition.to_value or (flt(condition.from_value) <= flt(value) <= flt(condition.to_value)):
 				return condition.shipping_amount
 
 		return 0.0