feat: add input validation for messages field (#4328)

Author: carenthomas

letta/helpers/message_helper.py

@@ -40,8 +40,7 @@ def _convert_message_create_to_message(
     assert isinstance(message_create, MessageCreate)
 
     # Extract message content
-    if isinstance(message_create.content, str):
-        assert message_create.content != "", "Message content must not be empty"
+    if isinstance(message_create.content, str) and message_create.content != "":
         message_content = [TextContent(text=message_create.content)]
     elif isinstance(message_create.content, list) and len(message_create.content) > 0:
         message_content = message_create.content

letta/server/rest_api/routers/v1/agents.py

@@ -1072,6 +1072,8 @@ async def send_message(
     Process a user message and return the agent's response.
     This endpoint accepts a message from a user and processes it through the agent.
     """
+    if len(request.messages) == 0:
+        raise ValueError("Messages must not be empty")
     request_start_timestamp_ns = get_utc_timestamp_ns()
     MetricRegistry().user_message_counter.add(1, get_ctx_attributes())