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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 fetch(self):
 """ Fetch a InstalledAddOnExtensionInstance :returns: Fetched InstalledAddOnExtensionInstance :rtype: twilio.rest.preview.marketplace.installed_add_on.installed_add_on_extension.InstalledAddOnExtensionInstance """

        params = values.of({})

        payload = self._version.fetch(
            'GET',
            self._uri,
            params=params,
        )

        return InstalledAddOnExtensionInstance(
            self._version,
            payload,
            installed_add_on_sid=self._solution['installed_add_on_sid'],
            sid=self._solution['sid'],
        )