Describe the bug

Upon the next prompt (after the empty one), we get an error message:

ERROR goose::agents::truncate: Error: Request failed: Request failed with status: 400 Bad Request. Message: * GenerateContentRequest.contents[0].parts: contents.parts must not be empty.

    at crates/goose/src/agents/truncate.rs:279

I put a sample interaction in the following log file: error_when_empty_prompt.log

To Reproduce

1. Start a session with Goose using the Gemini API.
2. Leave the prompt empty or press enter.
3. Send any non-empty prompt, eg 'hello'. The error message is then printed. No LLM response is printed.

Expected behavior

The system should handle empty prompts gracefully.

Screenshots

(Not applicable as it's a CLI-based interaction).

Please provide following information:

• OS & Arch: Ubuntu 22.04, Linux x86
• Interface: CLI
• Version: 1.0.3
• Extensions enabled: Computer Controller, Developer
• Provider & Model: Google - gemini-2.0-flash-exp

Additional context

Based on the log, the error is identified at crates/goose/src/agents/truncate.rs:279, suggesting the error is on the server side where the request is not properly validated for empty content before processing.

I have only tested models gemini-2.0-flash-exp and gpt-4o. The gemini one has this problem, the gpt-4o one works fine.