public AggregationExpression(Type type, Expression expression, AggregationModifier aggregationModifier)
            : base(ArgumentUtility.CheckNotNull("type", type))
        {
            ArgumentUtility.CheckNotNull("expression", expression);

            _expression          = expression;
            _aggregationModifier = aggregationModifier;
        }
    public AggregationExpression (Type type, Expression expression, AggregationModifier aggregationModifier)
        : base (ArgumentUtility.CheckNotNull ("type", type)) 
    {
      ArgumentUtility.CheckNotNull ("expression", expression);

      _expression = expression;
      _aggregationModifier = aggregationModifier;
    }