diff --git a/packages/client/src/tiptap/prose-utils/url.ts b/packages/client/src/tiptap/prose-utils/url.ts
index e351802..0c0b984 100644
--- a/packages/client/src/tiptap/prose-utils/url.ts
+++ b/packages/client/src/tiptap/prose-utils/url.ts
@@ -1,3 +1,3 @@
 export function isValidURL(str: string) {
-  return str.startsWith('http');
+  return str && str.startsWith('http');
 }