Fix bug where to_lucene is mistakenly called on nil when Arrays or Hashes are empty. Rename BooleanOperator to InfixOperator.
Fix bug where to_lucene is mistakenly called on nil when Arrays or Hashes are empty. Rename BooleanOperator to InfixOperator.

copyhacker/lucene_query,jvoorhis/lucene_query,ukasiu/lucene_query