public void setMerkleTreeConfig(MerkleTreeConfig merkleTreeConfig) {
        this.merkleTreeConfig = checkNotNull(merkleTreeConfig, "merkleTreeConfig cannot be null!");
    }
@Test(expected = NullPointerException.class)
    public void givenNullMerkleTreeConfig_throws_NPE() {
        new CacheConfig()
                .setMerkleTreeConfig(null);
    }