Fix no response / null response from LLM

[Vidit-Ostwal]

This is a try solution for None / Empty response from LLM.

This PR assumes that this might be because of context length exceeded at the server side, which is not returning an error, just an empty response.
This PR captures the ValueError which is being raised and try again with summarization.

---

Note

Detect None/empty LLM responses as context-window overflows, trigger summarization/retry in executors, add utility and tests, and refine type hints.

• Error handling & resilience
  • Treat ValueError with empty/None LLM responses as potential context overflow via new is_null_response_because_context_length_exceeded.
  • Update executors (crewai/agents/crew_agent_executor.py, crewai/lite_agent.py) to handle this case alongside is_context_length_exceeded, invoking handle_context_length to summarize and retry.
  • Enhance agent_utils.is_context_length_exceeded signature/docs; keep core detection; add LLMMessage typing usage.
• Utilities
  • Add is_null_response_because_context_length_exceeded(exception, messages, llm) in agent_utils.py to infer overflow by chunking messages against llm.get_context_window_size().
• Typing/Interfaces
  • Use BaseAgent in TaskEvaluator and broaden tool execution types to accept Agent | BaseAgent.
• Tests
  • New tests validating empty-response overflow handling in agent execution and the new utility (tests/agents/test_agent.py, tests/utilities/test_agent_utils.py).

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[Vidit-Ostwal]

Hey @lucasgomide, do you think this could be possible solution for this?
#2885 (comment)

I got some feedback from folks who tried the feature branch

• [BUG] Invalid response from LLM call - None or empty. #2885 (comment)
• [BUG] Invalid response from LLM call - None or empty. #2885 (comment)

[Vidit-Ostwal]

Gentle ping on this one @lucasgomide

[lucasgomide]

Added to my list to review later today

[lucasgomide]

mind you checking the CI errors?

[Vidit-Ostwal]

mind you checking the CI errors?

All fixed now.