[NTG-context] Bug in export with \definehighlight

Compiling the following document ~~~ \definehighlight [object] [style=mono] \setupbackend [export=yes] \starttext \object{test} \stoptext ~~~ gives backend > export > saving xml data in 'test.export backend > export > saving css image definitions in 'test-images.css backend > export > saving css style definitions in 'test-styles.css ! LuaTeX error bad argument #3 to '?' (value expected). system > tex > error on line 0 in file : LuaTeX error ... <empty file> <*> ./test \stoptext Aditya