Detail page of demo site logs a QueryException for comments Car pages in faceted navigation environment

2010-08-12 12:24:31,840 [19088089@qtp-33379524-3] WARN org.hippoecm.hst.demo.components.Detail - QueryException
org.hippoecm.hst.content.beans.query.exceptions.FilterException: Not allowed to search on 'null'.
at org.hippoecm.hst.content.beans.query.filter.FilterImpl.addEqualTo(FilterImpl.java:123)
at org.hippoecm.hst.utils.BeanUtils.createIncomingBeansQuery(BeanUtils.java:95)
at org.hippoecm.hst.utils.BeanUtils.createIncomingBeansQuery(BeanUtils.java:55)
at org.hippoecm.hst.demo.components.Detail.doBeforeRender(Detail.java:93)
at org.hippoecm.hst.core.container.HstComponentInvokerImpl.invokeBeforeRender(HstComponentInvokerImpl.java:116)
at sun.reflect.GeneratedMethodAccessor39.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:77)