private void checkElt(final String what, final int expectedSize) {
    checkElt(what);
    if (currentPayloadSize != expectedSize)
      throw error(
          "Cannot read a %s, expecting %d bytes but current element is %d bytes long",
          what, expectedSize, currentPayloadSize);
  }
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