code: private List<IndexExpression> getIndexExpressions() throws IOException
      {
          UDFContext context = UDFContext.getUDFContext();
          Properties property = context.getUDFProperties(AbstractCassandraStorage.class);
          if (property.getProperty(PARTITION_FILTER_SIGNATURE) != null)
              return indexExpressionsFromString(property.getProperty(PARTITION_FILTER_SIGNATURE));
          else
              return null;
      }
docs: get a list of index expression