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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 call(self, jsondata):
 """ Calls jsonrpc service's method and returns its return value in a JSON string or None if there is none. Arguments: jsondata -- remote method call in jsonrpc format """

        result = yield self.call_py(jsondata)
        if result is None:
            defer.returnValue(None)
        else:
            defer.returnValue(json.dumps(result))