from typing import Optional


def validate_self_discharge(self_discharge: Optional[float]) -> Optional[float]:
    """
    Validates the self discharge of an object.
    Self discharge is always optional.

    :param self_discharge: The self discharge of the object.
    :return: The validated self discharge.
    """
    if self_discharge is None:
        return None

    if self_discharge < 0 or self_discharge > 1:
        raise ValueError("Self discharge must be between 0 and 1.")

    return self_discharge