public BlockOptions setExtraData(final Bytes extraData) {
      this.extraData = Optional.of(extraData);
      return this;
    }
Creates a byte sequence with leading zeros.

@param size The size of the byte array to return
@param zerofill The number of lower-order bytes to fill with zero (creating a smaller big
    endian integer value)
@return the array of bytes.
ethereum/core/src/test-support/java/org/hyperledger/besu/ethereum/core/BlockDataGenerator.java