minor fix in website sitemap

frappe/website/doctype/website_sitemap/website_sitemap.py

@@ -37,7 +37,7 @@ class DocType(DocTypeNestedSet):
 				where parent_website_sitemap=%s and name!=%s""", (self.doc.parent_website_sitemap,
 					self.doc.name))[0][0] or 0) + 1
 		else:
-			if self.doc.idx != 0:
+			if self.doc.idx != 0 and self.doc.parent_website_sitemap:
 				if not frappe.conn.get_value("Website Sitemap", {
 					"idx": self.doc.idx -1, 
 					"parent_website_sitemap":self.doc.parent_website_sitemap