from typing import Optional


def validate_conversion_factor(conversion_factor: Optional[float]) -> Optional[float]:
    """
    Validates the conversion factor of an object.
    Conversion factor is always optional.

    :param conversion_factor: The conversion factor of the object.
    :return: The validated conversion factor.
    """
    if conversion_factor is None:
        # Skip validation if no value provided
        return None
    if conversion_factor < -5 or conversion_factor > 5:
        raise ValueError("Conversion factor must be between -5 and 5.")

    return conversion_factor