Always use explicit null checks (`value is None` or `value is not None`) rather than implicit truthiness evaluations when testing for null/None values. Implicit boolean checks can invoke `__bool__` methods leading to unexpected behavior. **Do this:** ```python # Explicitly check if out is not None if out is not None: # Use out process(out) ``` **Not this:** ```python # Don't rely on truthiness which may call __bool__ if out: # May not behave as expected if __bool__ is implemented process(out) ``` For complex types that can represent optional values, use proper optional type wrappers: In C++: ```cpp // Use optional wrappers for nullable types 'float or None': 'dmlc::optional' // Instead of just 'mx_float' ``` When handling values that might have multiple return types or be null: ```python # Check the specific type before processing if isinstance(out, NDArrayBase): return out return list(out) # Convert if needed ```