def certify_required(value, required=False):
    """
    Certify that a value is present if required.

    :param object value:
        The value that is to be certified.
    :param bool required:
        Is the value required?
    :raises CertifierValueError:
        Required value is `None`.

    """
    # Certify our kwargs:
    if not isinstance(required, bool):
        raise CertifierParamError(
            'required',
            required,
        )
    if value is None:
        if required:
            raise CertifierValueError(
                message="required value is None",
            )
        return True