Problem using nullValue in parameter map

[Peter Martin]

I have a parameterMap that is using a "map" object. If it doesn't  
find the property in the map I want nullValue to provide the value.   
This isn't working for me, should this be OK? I am using iBATIS 2.3.0.

        <parameterMap id="countPeopleParameters" class="map">
		<parameter property="result" javaType="int" jdbcType="INTEGER"  
mode="OUT" />
		<parameter property="lastName" javaType="string" jdbcType="VARCHAR"  
mode="IN" nullValue="%" />
        </parameterMap>

Thanks
Peter.