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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_min_isr(zk, topic):
 """Return the min-isr for topic, or None if not specified"""

    ISR_CONF_NAME = 'min.insync.replicas'
    try:
        config = zk.get_topic_config(topic)
    except NoNodeError:
        return None
    if ISR_CONF_NAME in config['config']:
        return int(config['config'][ISR_CONF_NAME])
    else:
        return None