Zend_Search_Lucene and range search

Question

I have a bunch of int key fields in my index and trying to do a simple range search like this:

`gender:1 AND height:[120 TO 180]`

This should give me male in the height range 120 to 180. But for some reason i get this exception:

`At least one range query boundary term must be non-empty term`

How would i debug this? Is it just Zend_Search_Lucene being buggy?