fix: using db.exists and get_value instead of get_doc
diff --git a/erpnext/erpnext_integrations/doctype/taxjar_settings/taxjar_settings.py b/erpnext/erpnext_integrations/doctype/taxjar_settings/taxjar_settings.py
index 4082783..dd83c17 100644
--- a/erpnext/erpnext_integrations/doctype/taxjar_settings/taxjar_settings.py
+++ b/erpnext/erpnext_integrations/doctype/taxjar_settings/taxjar_settings.py
@@ -25,9 +25,9 @@
 
 		custom_fields = []
 		for dt in ['Item', 'Sales Invoice Item']:
-			doc = frappe.get_doc('Custom Field', {'dt': dt, 'fieldname':'product_tax_category'})
+			doc = frappe.db.exists('Custom Field', {'dt': dt, 'fieldname':'product_tax_category'})
 			custom_fields.append(doc)
-			fields_hidden = doc.get('hidden') if doc else 0
+			fields_hidden = frappe.db.get_value('Custom Field', {'dt': dt, 'fieldname':'product_tax_category'},'hidden')
 		fields_already_exist = True if custom_fields else False