diff --git a/utils/string-utils.class.ts b/utils/string-utils.class.ts
index 1f24592f..f71cdc3e 100644
--- a/utils/string-utils.class.ts
+++ b/utils/string-utils.class.ts
@@ -284,7 +284,7 @@ export class StringUtils {
   public static jsonRegex = /^[\],:{}\s]*$/;
   
   public static urlPrefix(url: string): string {
-    if (url.startsWith("http://") || url.startsWith("https://") || url.startsWith("//")) {
+    if (!url || url.startsWith("http://") || url.startsWith("https://") || url.startsWith("//")) {
       return "";
     } else {
       return "//";