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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 service_headline(self, short_name):
 """Get the headline stored for a service. Args: short_name (string):
 The short name of the service to get messages for Returns: ServiceMessage: the headline or None if there is no headline """


        if short_name not in self.services:
            raise ArgumentError("Unknown service name", short_name=short_name)

        return self.services[short_name]['state'].headline