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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 get_instance(cls, device):
 """ This is only a slot to store and get already initialized poco instance rather than initializing again. You can simply pass the ``current device instance`` provided by ``airtest`` to get the AndroidUiautomationPoco instance. If no such AndroidUiautomationPoco instance, a new instance will be created and stored. Args: device (:py:obj:`airtest.core.device.Device`):
 more details refer to ``airtest doc`` Returns: poco instance """


        if cls._nuis.get(device) is None:
            cls._nuis[device] = AndroidUiautomationPoco(device)
        return cls._nuis[device]