Update app.py

app.py

@@ -21,7 +21,7 @@ This tool lets you check if a repository under a given username is part of The S
 
 def check_username(username):
     output_md = ""
-    if username in usernames:
+    if username in usernames and len(usernames[username])>0:
         repos = usernames[username]
         repo_word = "repository" if len(repos)==1 else "repositories"
         output_md += f"**Yes**, there is code from **{len(repos)} {repo_word}** in The Stack:\n\n"