Spring + Ehcache : Not able to get the cache back from cacheManager without key

I am using Spring + Ehcache for my cache layer and it is working. But for some reason I wanna manipulate the cache manually.

Code:

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@Cacheable(value = "productAll")
public List<Product> getAllProduct()

@CacheEvict(value = "product", key = "#product.id")
public Product saveProduct(Product product)

@Cacheable(value = "product")
public Product getProductById(Long id)

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These works fine.. but when I try to manually update the productAll cache in the saveProduct function. I am not able to get the cache back from the cache manager

Code:

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Cache cache = cacheManager.getCache("productAll");
cache.get("");

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What is the key that I should use in this case when no key is provided when we cache in the getProductAll method?

Please advise Thanks in advance!