title: SOLR query, value of field 1 is same as field 2, OR field 1 is empty
body: <p>Got a SOLR query question here, how do I construct my query to suit the following condition:</p>
  
  <p>(value of field 1 is same as field 2) OR (field 1 is empty)</p>
  
  <p>Cheers</p>
  
  <p>James</p>