fix: empty usage (#2168)

api/core/features/assistant_cot_runner.py

@@ -298,7 +298,7 @@ class AssistantCotApplicationRunner(BaseAssistantApplicationRunner):
             message=AssistantPromptMessage(
                 content=final_answer
             ),
-            usage=llm_usage['usage'],
+            usage=llm_usage['usage'] if llm_usage['usage'] else LLMUsage.empty_usage(),
             system_fingerprint=''
         ), PublishFrom.APPLICATION_MANAGER)
 

api/core/features/assistant_fc_runner.py

@@ -276,7 +276,7 @@ class AssistantFunctionCallApplicationRunner(BaseAssistantApplicationRunner):
             message=AssistantPromptMessage(
                 content=final_answer,
             ),
-            usage=llm_usage['usage'],
+            usage=llm_usage['usage'] if llm_usage['usage'] else LLMUsage.empty_usage(),
             system_fingerprint=''
         ), PublishFrom.APPLICATION_MANAGER)