fix: validate theme_scss attribute
diff --git a/erpnext/public/js/website_theme.js b/erpnext/public/js/website_theme.js
index 84de2f5..9662f78 100644
--- a/erpnext/public/js/website_theme.js
+++ b/erpnext/public/js/website_theme.js
@@ -4,8 +4,8 @@
 frappe.ui.form.on('Website Theme', {
 	validate(frm) {
 		let theme_scss = frm.doc.theme_scss;
-		if (theme_scss.includes('frappe/public/scss/website')
-			&& !theme_scss.includes('erpnext/public/scss/website')
+		if (theme_scss && (theme_scss.includes('frappe/public/scss/website')
+			&& !theme_scss.includes('erpnext/public/scss/website'))
 		) {
 			frm.set_value('theme_scss',
 				`${frm.doc.theme_scss}\n@import "erpnext/public/scss/website";`);