Cannot resolve 'oidcext:OIDCString' as a QName

[McLennan, Neil R]

Installing idp-oidc-extension-distribution-2.0.0.zip then following instructions at https://github.com/CSCfi/shibboleth-idp-oidc-extension/wiki/Installing-from-archive  and then built.bat

I add the example into attributer-filer.xml

    <AttributeFilterPolicy id="OPENID_SCOPE_EMAIL">
        <PolicyRequirementRule xsi:type="oidcext:OIDCString" value="email" />
        <AttributeRule attributeID="email">
            <PermitValueRule xsi:type="ANY" />
        </AttributeRule>
        <AttributeRule attributeID="email_verified">
            <PermitValueRule xsi:type="ANY" />
        </AttributeRule>
    </AttributeFilterPolicy>

And get the error ; UndeclaredPrefix: Cannot resolve 'oidcext:OIDCString' as a QName: the prefix 'oidcext' is not declared.

Line 30 in XML document from file [C:\Program Files (x86)\Shibboleth\IdP\conf\attribute-filter.xml] is invalid; nested exception is org.xml.sax.SAXParseException; lineNumber: 30; columnNumber: 78; UndeclaredPrefix: Cannot resolve 'oidcext:OIDCString' as a QName: the prefix 'oidcext' is not declared.
	at net.shibboleth.ext.spring.service.ReloadableSpringService.doReload(ReloadableSpringService.java:377)
Caused by: org.springframework.beans.factory.xml.XmlBeanDefinitionStoreException: Line 30 in XML document from file [C:\Program Files (x86)\Shibboleth\IdP\conf\attribute-filter.xml] is invalid; nested exception is org.xml.sax.SAXParseException; lineNumber: 30; columnNumber: 78; UndeclaredPrefix: Cannot resolve 'oidcext:OIDCString' as a QName: the prefix 'oidcext' is not declared.
	at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(XmlBeanDefinitionReader.java:400)

What have I misconfigured?