ft:thesaurus-lookup() on a non-existant word fails assertion

[Paul J. Lucas]

A query such as:

import module namespace ft = "http://www.zorba-xquery.com/modules/full-text";
declare ft-option using language "en";
ft:thesaurus-lookup( "hup" )

results in:

Zorba error [zerr:ZXQP0002]: "state->tresult_.get()": assertion failed.; raised at /Users/pjl/src/flwor/zorba/repo/trunk/zorba/src/runtime/full_text/ft_module_impl.cpp:508