diff --git a/src/file/table-of-contents/sdt-properties.ts b/src/file/table-of-contents/sdt-properties.ts
index f1f2c56304..998167d22a 100644
--- a/src/file/table-of-contents/sdt-properties.ts
+++ b/src/file/table-of-contents/sdt-properties.ts
@@ -2,8 +2,10 @@
 import { StringValueElement, XmlComponent } from "@file/xml-components";
 
 export class StructuredDocumentTagProperties extends XmlComponent {
-    public constructor(alias: string) {
+    public constructor(alias?: string) {
         super("w:sdtPr");
-        this.root.push(new StringValueElement("w:alias", alias));
+        if(typeof alias === 'string'){
+            this.root.push(new StringValueElement("w:alias", alias));
+        }
     }
 }