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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 update_cache_key(cls, cache_key, item=None):
 """Get item in cache for cache_key and add item if item is not None. """

        contents = cls.__thread_id_cache.get(cache_key, None)
        if item is not None:
            cls.__thread_id_cache[cache_key] = item

        return contents