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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 create_shortlink(self, callback_uri=None, description=None, serial_number=None):
 """Register new shortlink Arguments: callback_uri: URI called by mCASH when user scans shortlink description: Shortlink description displayed in confirmation dialogs serial_number: Serial number on printed QR codes. This field is only used when registering printed stickers issued by mCASH """

        arguments = {'callback_uri': callback_uri,
                     'description': description,
                     'serial_number': serial_number}
        return self.do_req('POST', self.merchant_api_base_url + '/shortlink/',
                           arguments).json()