code: public void addFields(Document document, Columns columns) {
          for (Column column : columns) {
              String name = column.getName();
              ColumnMapper columnMapper = getMapper(name);
              if (columnMapper != null) {
                  for (IndexableField field : columnMapper.fields(column)) {
                      document.add(field);
                  }
              }
          }
      }
docs: Adds to the specified {@link org.apache.lucene.document.Document} the Lucene fields representing the specified
  {@link com.stratio.cassandra.index.schema.Columns}.
  
  @param document The Lucene {@link org.apache.lucene.document.Document} where the fields are going to be added.
  @param columns  The {@link com.stratio.cassandra.index.schema.Columns} to be added.