### Question:
BlockStore { public synchronized Block getBlockByHash(byte[] hash) { return this.blocks.get(new Keccak256(hash)); }  synchronized void saveBlock(Block block); synchronized void removeBlock(Block block); synchronized Block getBlockByHash(byte[] hash); synchronized List<Block> getBlocksByNumber(long number); synchronized List<Block> getBlocksByParentHash(Keccak256 hash); List<Block> getChildrenOf(Set<Block> blocks); synchronized boolean hasBlock(Block block); synchronized boolean hasBlock(byte[] hash); synchronized int size(); synchronized long minimalHeight(); synchronized long maximumHeight(); synchronized void releaseRange(long from, long to); synchronized boolean hasHeader(Keccak256 hash); synchronized void saveHeader(@Nonnull final BlockHeader header); synchronized void removeHeader(@Nonnull final BlockHeader header);  }### Answer:
@Test public void getUnknownBlockAsNull() { BlockStore store = new BlockStore(); Assert.assertNull(store.getBlockByHash(TestUtils.randomBytes(32))); }