src/Adapter/MemoryCacheItemPool.php
public function getItem($key)
    {
        if ($this->hasItem($key) !== true) {
            $this->data[$key] = new CacheItem($key, null, false);
        }
        
        return $this->data[$key];
    }
public function getItem($key)
    {
        if ($this->hasItem($key) !== true) {
            $this->data[$key] = new CacheItem($key, null, false);
        }
        
        return $this->data[$key];
    }
Returns a Cache Item representing the specified key.

This method must always return a CacheItemInterface object, even in case of
a cache miss. It MUST NOT return null.

@param string $key
The key for which to return the corresponding Cache Item.

@throws InvalidArgumentException If the $key string is not a legal value a \Psr\Cache\InvalidArgumentException
MUST be thrown.

@return CacheItemInterface