The discovery-option "module" attribute should support undefined values

        <xs:attribute name="module" type="xs:string" use="optional">
            <xs:annotation>
                <xs:documentation>
                    The module from which the DiscoveryOption implementation should be loaded. If not provided,
                    the DiscoveryOption implementation must be available from the Host Controller's own module.
                </xs:documentation>
            </xs:annotation>
        </xs:attribute>