fix: dont validate empty category
diff --git a/erpnext/accounts/doctype/sales_taxes_and_charges_template/sales_taxes_and_charges_template.py b/erpnext/accounts/doctype/sales_taxes_and_charges_template/sales_taxes_and_charges_template.py
index 1d30934..8043a1b 100644
--- a/erpnext/accounts/doctype/sales_taxes_and_charges_template/sales_taxes_and_charges_template.py
+++ b/erpnext/accounts/doctype/sales_taxes_and_charges_template/sales_taxes_and_charges_template.py
@@ -55,5 +55,8 @@
 		frappe.throw(_("Disabled template must not be default template"))
 
 def validate_for_tax_category(doc):
+	if not doc.tax_category:
+		return
+
 	if frappe.db.exists(doc.doctype, {"company": doc.company, "tax_category": doc.tax_category, "disabled": 0, "name": ["!=", doc.name]}):
 		frappe.throw(_("A template with tax category {0} already exists. Only one template is allowed with each tax category").format(frappe.bold(doc.tax_category)))