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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_device_id(handler_input):
 # type: (HandlerInput) -> Optional[AnyStr] """Return the device id from the input request. The method retrieves the `deviceId` property from the input request. This value uniquely identifies the device and is generally used as input for some Alexa-specific API calls. More information about this can be found here : https://developer.amazon.com/docs/custom-skills/request-and-response-json-reference.html#system-object If there is no device information in the input request, then a ``None`` is returned. :param handler_input: The handler input instance that is generally passed in the sdk's request and exception components :type handler_input: ask_sdk_core.handler_input.HandlerInput :return: Unique device id of the device used to send the alexa request or `None` if device information is not present :rtype: Optional[str] """

    device = handler_input.request_envelope.context.system.device
    if device:
        return device.device_id
    else:
        return None