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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 getWorksheet(self):
 """Returns the Worksheet to which this analysis belongs to, or None """

        worksheet = self.getBackReferences('WorksheetAnalysis')
        if not worksheet:
            return None
        if len(worksheet) > 1:
            logger.error(
                "Analysis %s is assigned to more than one worksheet."
                % self.getId())
        return worksheet[0]