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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add(self, statisticType, onStatisticField, outStatisticFieldName=None):
 """ Adds the statistics group to the filter. outStatistics - is supported on only those layers/tables that indicate supportsStatistics is true. outStatisticFieldName is empty or missing, the map server assigns a field name to the returned statistic field. A valid field name can only contain alphanumeric characters and an underscore. outStatisticFieldName is a reserved keyword of the underlying DBMS, the operation can fail. Try specifying an alternative outStatisticFieldName. When using outStatistics, the only other parameters that can be used are groupByFieldsForStatistics, orderByFields, time, and where. """

        val = {
            "statisticType" : statisticType,
            "onStatisticField" : onStatisticField,
            "outStatisticFieldName" : outStatisticFieldName
        }
        if outStatisticFieldName is None:
            del val['outStatisticFieldName']
        self._array.append(val)