fix: type casting for None type value
diff --git a/erpnext/accounts/doctype/pos_invoice/pos_invoice.py b/erpnext/accounts/doctype/pos_invoice/pos_invoice.py
index 92fa5ef..402d157 100644
--- a/erpnext/accounts/doctype/pos_invoice/pos_invoice.py
+++ b/erpnext/accounts/doctype/pos_invoice/pos_invoice.py
@@ -57,7 +57,7 @@
 			self.apply_loyalty_points()
 		self.check_phone_payments()
 		self.set_status(update=True)
-	
+
 	def before_cancel(self):
 		if self.consolidated_invoice and frappe.db.get_value('Sales Invoice', self.consolidated_invoice, 'docstatus') == 1:
 			pos_closing_entry = frappe.get_all(
@@ -221,7 +221,7 @@
 		base_grand_total = flt(self.base_rounded_total) or flt(self.base_grand_total)
 		if not flt(self.change_amount) and grand_total < flt(self.paid_amount):
 			self.change_amount = flt(self.paid_amount - grand_total + flt(self.write_off_amount))
-			self.base_change_amount = flt(self.base_paid_amount - base_grand_total + flt(self.base_write_off_amount))
+			self.base_change_amount = flt(self.base_paid_amount) - base_grand_total + flt(self.base_write_off_amount)
 
 		if flt(self.change_amount) and not self.account_for_change_amount:
 			frappe.msgprint(_("Please enter Account for Change Amount"), raise_exception=1)
@@ -376,7 +376,7 @@
 				"campaign": profile.get("campaign"),
 				"allow_print_before_pay": profile.get("allow_print_before_pay")
 			}
-	
+
 	def reset_mode_of_payments(self):
 		if self.pos_profile:
 			pos_profile = frappe.get_cached_doc('POS Profile', self.pos_profile)
@@ -406,7 +406,7 @@
 					pay_req.request_phone_payment()
 
 				return pay_req
-	
+
 	def get_new_payment_request(self, mop):
 		payment_gateway_account = frappe.db.get_value("Payment Gateway Account", {
 			"payment_account": mop.account,