feat: improve error handling in _interpolate_only method

- Add comprehensive docstring with examples
- Add error handling for edge cases
- Add test cases for error scenarios

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

tests/agent_test.py

@@ -1383,6 +1383,25 @@ def test_interpolate_inputs_with_tool_description():
     })
     assert "Tool Arguments: {'arg': {'description': 'test arg', 'type': 'str'}}" in agent.backstory
 
+def test_interpolate_only_error_handling():
+    agent = Agent(
+        role="{topic} specialist",
+        goal="Figure {goal} out",
+        backstory="I am the master of {role}",
+    )
+    
+    # Test empty input string
+    with pytest.raises(ValueError, match="Input string cannot be None or empty"):
+        agent._interpolate_only("", {"topic": "AI"})
+        
+    # Test empty inputs dictionary
+    with pytest.raises(ValueError, match="Inputs dictionary cannot be empty"):
+        agent._interpolate_only("test {topic}", {})
+        
+    # Test missing template variable
+    with pytest.raises(KeyError, match="Missing required template variable"):
+        agent._interpolate_only("test {missing}", {"topic": "AI"})
+
 def test_agent_with_all_llm_attributes():
     agent = Agent(
         role="test role",