@Override
public Double getExpressionValue( Expression expression, Map<? extends DimensionalItemObject, Double> valueMap,
Map<String, Double> constantMap, Map<String, Integer> orgUnitCountMap, Integer days,
ListMap<String, Double> aggregateMap )
{
String expressionString = generateExpression( expression.getExpression(),
valueMap, constantMap, orgUnitCountMap, days, expression.getMissingValueStrategy(),
aggregateMap );
return expressionString != null ? calculateExpression( expressionString ) : null;
}