1) strictly speaking there is no such thing as a NULL field value in Solr -- there are fields that have a value and fields that don't and as mentioned yourField:[* TO *] will give you all docs that have a value in the yourField field.
2) http://people.apache.org/~hossman/#threadhijack Thread Hijacking on Mailing Lists When starting a new discussion on a mailing list, please do not reply to an existing message, instead start a fresh email. Even if you change the subject line of your email, other mail headers still track which thread you replied to and your question is "hidden" in that thread and gets less attention. It makes following discussions in the mailing list archives particularly difficult. See Also: http://en.wikipedia.org/wiki/Thread_hijacking -Hoss
