Fix #2740: Add validation for empty messages lists to prevent IndexError in LiteLLM's ollama_pt()

Co-Authored-By: Joe Moura <joao@crewai.com>

tests/test_empty_messages.py

@@ -0,0 +1,30 @@
+import pytest
+from unittest.mock import patch
+
+from crewai.llm import LLM
+
+
+def test_empty_messages_validation():
+    """
+    Test that LLM.call() raises a ValueError when an empty messages list is passed.
+    This prevents the IndexError in LiteLLM's ollama_pt() function.
+    """
+    llm = LLM(model="gpt-3.5-turbo")  # Any model will do for this test
+    
+    with pytest.raises(ValueError, match="Messages list cannot be empty"):
+        llm.call(messages=[])
+    
+    with pytest.raises(ValueError, match="Messages list cannot be empty"):
+        llm.call(messages=None)
+
+
+@pytest.mark.vcr(filter_headers=["authorization"])
+def test_ollama_model_empty_messages():
+    """
+    Test that LLM.call() with an Ollama model raises a ValueError 
+    when an empty messages list is passed.
+    """
+    llm = LLM(model="ollama/llama3")
+    
+    with pytest.raises(ValueError, match="Messages list cannot be empty"):
+        llm.call(messages=[])