'Returns the most recently received value for the given control number.
Args:
control_number: The integer control number to return the value for, or
None.
Returns:
The most recently recieved integer value for the given control number, or
None if no values have been received for that control.'

@concurrency.serialized
def control_value(self, control_number):

    if (control_number is None):
        return None
    return self._control_values.get(control_number)
