code: int removeDocument(final Term idTerm) throws IOException
     {
        try {
          return getIndexReader().deleteDocuments(idTerm);
        } catch (FileNotFoundException e) {
          log.debug("Document '" + idTerm + "' wasn't found, ignore document removal");
          return 0;
        }
     }
docs: Removes the document from this index. This call will not invalidate
  the shared reader. If a subclass wishes to do so, it should overwrite
  this method and call {@link #invalidateSharedReader()}.
  
  @param idTerm the id term of the document to remove.
  @throws IOException if an error occurs while removing the document.
  @return number of documents deleted