Returns an ordered list of batches to inject at the beginning of the
        block. Can also return None if no batches should be injected.

        Args:
            previous_block (Block): The previous block.

        Returns:
            A list of batches to inject.

def block_start(self, previous_block):
        """Returns an ordered list of batches to inject at the beginning of the
        block. Can also return None if no batches should be injected.

        Args:
            previous_block (Block): The previous block.

        Returns:
            A list of batches to inject.
        """

        previous_header_bytes = previous_block.header
        previous_header = BlockHeader()
        previous_header.ParseFromString(previous_header_bytes)

        block_info = BlockInfo(
            block_num=previous_header.block_num,
            previous_block_id=previous_header.previous_block_id,
            signer_public_key=previous_header.signer_public_key,
            header_signature=previous_block.header_signature,
            timestamp=int(time.time()))

        return [self.create_batch(block_info)]