[Feature]: Handle one system message for Bedrock Anthropic models more gracefully

[PragyaTripathi]

The Feature

When one message with role system is passed, LiteLLM correctly extracts out system message to be sent as system parameter for Anthropic. However, it leaves with no messages left to LLM. The code throws exception which can be hard to decipher.
litellm/llms/prompt_templates/factory.py\", line 2401, in _bedrock_converse_messages_pt\n if messages[0].get(\"role\") is not None and messages[0][\"role\"] == \"assistant\":\nIndexError: list index out of range\n"

Motivation, pitch

LiteLLM's abstraction of message type passing for different LLMs is amazing. However, when there are issues like above, a more clear message would really help users to understand what has gone wrong and how to fix it.

Twitter / LinkedIn details

No response

[krrishdholakia]

great point - will get this done today