fix: None type in cot assistant app (#2142)

api/core/features/assistant_cot_runner.py

@@ -473,7 +473,7 @@ class AssistantCotApplicationRunner(BaseAssistantApplicationRunner):
 
         result = ''
         for scratchpad in agent_scratchpad:
-            result += scratchpad.thought + next_iteration.replace("{{observation}}", scratchpad.observation) + "\n"
+            result += scratchpad.thought + next_iteration.replace("{{observation}}", scratchpad.observation or '') + "\n"
 
         return result
     
@@ -543,7 +543,7 @@ class AssistantCotApplicationRunner(BaseAssistantApplicationRunner):
             # add assistant message
             if len(agent_scratchpad) > 0:
                 prompt_messages.append(AssistantPromptMessage(
-                    content=agent_scratchpad[-1].thought + "\n" + agent_scratchpad[-1].observation
+                    content=(agent_scratchpad[-1].thought or '') + "\n" + (agent_scratchpad[-1].observation or '')
                 ))
 
             # add user message

api/core/features/assistant_fc_runner.py

@@ -172,7 +172,6 @@ class AssistantFunctionCallApplicationRunner(BaseAssistantApplicationRunner):
             for tool_call_id, tool_call_name, tool_call_args in tool_calls:
                 tool_instance = tool_instances.get(tool_call_name)
                 if not tool_instance:
-                    logger.error(f"failed to find tool instance: {tool_call_name}")
                     tool_response = {
                         "tool_call_id": tool_call_id,
                         "tool_call_name": tool_call_name,
@@ -220,7 +219,6 @@ class AssistantFunctionCallApplicationRunner(BaseAssistantApplicationRunner):
 
                     if error_response:
                         observation = error_response
-                        logger.error(error_response)
                         tool_response = {
                             "tool_call_id": tool_call_id,
                             "tool_call_name": tool_call_name,