set None value for undefined LoD entries

[WolfgangFahl]

 def setNone4List(self,listOfDicts,fields):
        '''
        set the given fields to None for the records in the given listOfDicts
        if they are not set
        Args:
            listOfDicts(list): the list of records to work on
            fields(list): the list of fields to set to None 
        '''
        for record in listOfDicts:
            self.setNone(record, fields)
    
    def setNone(self,record,fields):
        '''
        make sure the given fields in the given record are set to none
        Args:
            record(dict): the record to work on
            fields(list): the list of fields to set to None 
        '''
        for field in fields:
            if not field in record:
                record[field]=None

but make sure a copy of the records is optionally used to keep the original list of dict as is.