Update app.py

app.py

@@ -476,12 +476,15 @@ def share(title, editor, cover_art):
       download_mode=DownloadMode.FORCE_REDOWNLOAD,
       verification_mode=VerificationMode.NO_CHECKS
   )
-    
-  buffered = io.BytesIO()
-  cover_art = Image.fromarray(cover_art.astype('uint8'))    
-  cover_art.save(buffered, format="JPEG")
-  img_str = base64.b64encode(buffered.getvalue())
 
+  if cover_art is not None:
+    buffered = io.BytesIO()
+    cover_art = Image.fromarray(cover_art.astype('uint8'))    
+    cover_art.save(buffered, format="JPEG")
+    img_str = base64.b64encode(buffered.getvalue())
+  else:
+    img_str = ""
+      
   dataset['train'] = dataset['train'].add_item({
       'title': title,
       'story': editor,