Check db url before attempting to get a user id.

src/lib/user-id.ts

@@ -32,5 +32,9 @@ export const parseDbUrl = (urlString: string) => {
   return { username: hex2a(encodedUser), database: urlString };
 };
 
-export const dbUrlToUserId = (urlString: string) =>
-  userId(parseDbUrl(urlString));
+export const dbUrlToUserId = (urlString: string) => {
+  if (!urlString) {
+    return null;
+  }
+  return userId(parseDbUrl(urlString));
+};