Given a block number returns the hex representation of the blockhash

def get(self, block_number: BlockNumber) -> str:
        """Given a block number returns the hex representation of the blockhash"""
        if block_number in self.mapping:
            return self.mapping[block_number]

        block_hash = self.web3.eth.getBlock(block_number)['hash']
        block_hash = block_hash.hex()
        self.mapping[block_number] = block_hash
        return block_hash