private int hexStringToInt(final String hexString) {
    return Bytes.fromHexStringLenient(hexString).toInt();
  }
Tests that empty batch requests are treated as invalid requests as per
http://www.jsonrpc.org/specification#batch.
ethereum/api/src/test/java/org/hyperledger/besu/ethereum/api/jsonrpc/JsonRpcHttpServiceTest.java