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 and treat None/empty LLM responses as context-window overflows, trigger summarization, and retry; add targeted tests and minor typing updates.

• Agents (execution loop):
  • Add is_null_response_because_context_length_exceeded(...) alongside is_context_length_exceeded(...) in CrewAgentExecutor and LiteAgent to detect empty responses likely caused by context overflow and invoke handle_context_length (summarization + retry).
• Utilities:
  • New is_null_response_because_context_length_exceeded(exception, messages, llm) in crewai/utilities/agent_utils.py (chunks messages by llm.get_context_window_size() and checks ValueError "None or empty").
  • Simplify is_context_length_exceeded(exception) signature and docs; wire LLMMessage typing in relevant modules.
• Evaluator/Tools:
  • Use BaseAgent in TaskEvaluator constructor typing; import BaseAgent in tool_utils.
• Tests:
  • Add tests for null/empty response handling path and for is_null_response_because_context_length_exceeded in tests/utilities/test_agent_utils.py.
  • Extend agent tests to validate summarization and final answer flow when empty responses occur.

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[Vidit-Ostwal]

Hey @lucasgomide, do you think this could be possible solution for this? https://github.com/crewAIInc/crewAI/issues/2885#issuecomment-3338740438

I got some feedback from folks who tried the feature branch

• https://github.com/crewAIInc/crewAI/issues/2885#issuecomment-3337343477
• https://github.com/crewAIInc/crewAI/issues/2885#issuecomment-3337359639

[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.