scripted attributes and customObjectRef="shibboleth.HttpServletRequest"

[Liam Hoekenga]

I'm trying to use the customObjectReg interface to
shibboleth.HttpServletRequest,

I'm using the RemoteUser authentication flow in Shibboleth IDP 3.3.1.
RHEL 6.9, Oracle java 1.8.0_131, Tomcat 8.0.43 fronted by Apache HTTPd
2.2.x and mod_proxy_ajp.

    <resolver:AttributeDefinition
xmlns="urn:mace:shibboleth:2.0:resolver:ad" xsi:type="Script" id="testAttr"
dependencyOnly="false" language="nashorn"
customObjectRef="shibboleth.HttpServletResponse">
        <resolver:Dependency ref="mcommDir"/>
        <Script><![CDATA[
            logger =
Java.type("org.slf4j.LoggerFactory").getLogger("net.shibboleth.idp.attribute.resolver.testAttr");
            logger.debug("***** " + custom.getHeader("User-Agent"));
            testAttr.addValue("value");
        ]]></Script>
    </resolver:AttributeDefinition>

Every method I try returns "null".

2017-06-13 16:06:14,207 - DEBUG
[net.shibboleth.idp.attribute.resolver.testAttr:2] - xxx.xxx.xxx.xxx  -
***** null


I thought I had the correct usage.   The "custom" variable shows that it's
of
type net.shibboleth.utilities.java.support.net.ThreadLocalHttpServletResponseProxy

Any suggestions?
Liam
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