Unable to submit request because it has an empty text parameter. Add a value to the parameter and try again. #697

Description of the bug:

chat_session.send_message() with empty parts fails with an error:

google.api_core.exceptions.InvalidArgument: 400 Unable to submit request because it has an empty text parameter. Add a value to the parameter and try again. Learn more: https://cloud.google.com/vertex-ai/generative-ai/docs/model-reference/gemini

This fails, which was working earlier
chat_session.send_message({'role': 'user', 'parts': ''});

where chat_session = ChatSession(model=model, history=history)

Actual vs expected behavior:

No response

Any other information you'd like to share?

No response