LRUCache.set not update cache value when the key exists

[CwjXFH]

LRUCache.set does not update the cache value when the key exists, this may confuse the user. Why is it designed this way?

def set(self, key: K, value: V):
    if self.cache.get(key):
        self.cache.move_to_end(key, last=True)
    else:
        self.cache[key] = value
        if self.capacity is not None and self.length > self.capacity:
            self.cache.popitem(last=False)