The GeoServer build is broken. Looks like recent GeoTools filter changes caused the problem. I have reopened the related GeoTools issue:
http://jira.codehaus.org/browse/GEOT-2226
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Ben Caradoc-Davies <Ben.Caradoc-Davies@anonymised.com>
Software Engineer, CSIRO Exploration and Mining
Australian Resources Research Centre
26 Dick Perry Ave, Kensington WA 6151, Australia