Fix typing: add null checks and safe access in agentic multiturn tutorial

Author: prassanna-ravishankar

examples/tutorials/10_agentic/00_base/010_multiturn/project/acp.py

@@ -97,13 +97,19 @@ async def handle_event_send(params: SendEventParams):
     #########################################################
 
     task_state = await adk.state.get_by_task_and_agent(task_id=params.task.id, agent_id=params.agent.id)
+    if not task_state:
+        raise ValueError("Task state not found - ensure task was properly initialized")
     state = StateModel.model_validate(task_state.state)
 
     #########################################################
     # 6. (👋) Add the new user message to the message history
     #########################################################
 
-    state.messages.append(UserMessage(content=params.event.content.content))
+    # Safely extract content from the event
+    content_text = ""
+    if hasattr(params.event.content, 'content') and isinstance(params.event.content.content, str):
+        content_text = params.event.content.content
+    state.messages.append(UserMessage(content=content_text))
 
     #########################################################
     # 7. (👋) Call an LLM to respond to the user's message
@@ -114,7 +120,8 @@ async def handle_event_send(params: SendEventParams):
         llm_config=LLMConfig(model="gpt-4o-mini", messages=state.messages),
         trace_id=params.task.id,
     )
-    state.messages.append(AssistantMessage(content=chat_completion.choices[0].message.content))
+    response_content = chat_completion.choices[0].message.content or ""
+    state.messages.append(AssistantMessage(content=response_content))
 
     #########################################################
     # 8. (👋) Send agent response to client