@Override
  public BigInteger readBigIntegerScalar() {
    checkScalar("arbitrary precision scalar");
    final BigInteger res = getUnsignedBigInteger(currentPayloadOffset, currentPayloadSize);
    setTo(nextItem());
    return res;
  }
Sets the input to the item provided (an offset to the beginning of an item) and check this is
valid.

@param item the value to which the current item is to be set.
ethereum/rlp/src/main/java/org/hyperledger/besu/ethereum/rlp/AbstractRLPInput.java