couch-lucene hwo to refernce elements in a complex document?

[Mike Kimber]

I have couch-lucene working when I index a top level element in my documents. 
However when I try and reference a sub element as I would with a couchdb view 
no results are returned. A extract from my document is:

{
   "_id": "00023157-c1f8-4e39-ab9a-d56726739b8d",
   "_rev": "1-45cd4f7506ccede344d682904556be4b",
   "type": "maven-build-profile",
   "schema": "TODO-idOfSchemaDocument",
   "headers": {
       "started": 1328795714442,
       "core": {
           "user": "buildadm",
           "ip": "127.0.0.1",
           "executionId": "a607c818-c568-40a9-adbc-0844e6bf9a02"
       }
}
}

The following works

{
   "_id": "_design/lucene",
   "_rev": "19-1c7be47e52f8a65e9bb387e8c3251dd4",
   "language": "javascript",
   "fulltext": {
       "by_type": {
           "index": "function(doc) { var res = new Document(); res.add( doc. 
type); return res; }"
       }
   }
}

curl 
http://127.0.0.1:5999/_fti/local/build-profiles-raw-mk/_design/lucene/by_type?q=
 maven-build-profile

The following does not:

{
   "_id": "_design/lucene",
   "_rev": "19-1c7be47e52f8a65e9bb387e8c3251dd4",
   "language": "javascript",
   "fulltext": {
       "by_user": {
           "index": "function(doc) { var res = new Document(); res.add( 
doc.headers.core.user ); return res; }"
       }
   }
}


curl 
http://127.0.0.1:5999/_fti/local/build-profiles-raw-mk/_design/lucene/by_user?q=buildadm

Log file wise it provides:

2012-05-16 21:33:01,980 WARN [build-profiles-raw-mk] _design/buildstats caused 
TypeError: Cannot read property "core" from undefined
2012-05-16 21:33:01,980 WARN [build-profiles-raw-mk] _design/buildstatsdetail 
caused TypeError: Cannot read property "core" from undefined
2012-05-16 21:33:02,062 WARN [build-profiles-raw-mk] _design/profiling caused 
TypeError: Cannot read property "core" from undefined
2012-05-16 21:33:02,063 WARN [build-profiles-raw-mk] _design/lucene caused 
TypeError: Cannot read property "core" from undefined
2012-05-16 21:33:17,039 INFO [build-profiles-raw-mk] 
View[name=_design/lucene/by_user, digest=482tp0k1h6vhiw1cs5humyido] now at 
update_seq 106

I'm sure there is an easy answer to this, but to a javascript/couchdb newbie 
i'm confused as to why I can use doc.headers.core.user can be used in my couch 
map. But not in the above couch-lucene index.

Thanks

Mike