Update app.py

Clear BASE_SYSTEM_MESSAGE if system_message is set

app.py

@@ -34,9 +34,16 @@ def user(message, history):
 def chat(history, system_message, max_tokens, temperature, top_p, top_k, repetition_penalty):
     history = history or []
 
-    messages = "<|im_start|>"+"system\n" + BASE_SYSTEM_MESSAGE + system_message.strip() + "<|im_end|>\n" + \
-               "\n".join(["\n".join(["<|im_start|>"+"user\n"+item[0]+"<|im_end|>", "<|im_start|>assistant\n"+item[1]+"<|im_end|>"])
-                          for item in history])
+    if system_message.strip():   
+        # if system_message is not None or empty
+        messages = "<|im_start|>"+"system\n" + system_message.strip() + "<|im_end|>\n" + \
+                   "\n".join(["\n".join(["<|im_start|>"+"user\n"+item[0]+"<|im_end|>", "<|im_start|>assistant\n"+item[1]+"<|im_end|>"])
+                              for item in history])
+    else:
+        # if system_message is None or empty, use BASE_SYSTEM_MESSAGE
+        messages = "<|im_start|>"+"system\n" + BASE_SYSTEM_MESSAGE + "<|im_end|>\n" + \
+                   "\n".join(["\n".join(["<|im_start|>"+"user\n"+item[0]+"<|im_end|>", "<|im_start|>assistant\n"+item[1]+"<|im_end|>"])
+                              for item in history])
     # strip the last `<|end_of_turn|>` from the messages
     messages = messages.rstrip("<|im_end|>")
     # remove last space from assistant, some models output a ZWSP if you leave a space