Update app.py

app.py

@@ -106,6 +106,8 @@ def zip_ims(g):
     if g is None:
         return None
     l = list(map(lambda x: x["name"], g))
+    if not l:
+        return None
     zip_file_name ="tmp.zip"
     with ZipFile(zip_file_name ,"w") as zipObj:
         for ele in l: