Update palmapi.py

palmapi.py

@@ -27,7 +27,7 @@ class PaLMChatPromptFmt(PromptFmt):
         ping = pingpong.ping[:truncate_size]
         pong = pingpong.pong
         
-        if pong is None:
+        if pong is None or pong.strip() == "":
             return [
                 {
                     "author": "USER",