code: @Override
  	public DataSet getNextDataSet(final String key) {
  		DataSet data = getNextDataSetImpl(key);
  		if (data != null) {
  			copyFixedValues(key, data);
  			currentDataSets.put(key, data);
  		}
  		return data;
  	}
docs: Returns the next {@link DataSet} for the specified key. Fixed values are applied to the
  result.
  
  @param key
  The key.
  @return The {@link DataSet}, or null, if none is available.