public long getTransactionCount(final Address address, final long blockNumber) {
    final Hash blockHash =
        getBlockHeaderByNumber(blockNumber).map(BlockHeader::getHash).orElse(Hash.EMPTY);

    return getTransactionCount(address, blockHash);
  }
Returns the number of transactions sent from the given address in the block at the given
height.

@param address The address whose sent transactions we want to count.
@param blockNumber The height of the block being queried.
@return The number of transactions sent from the given address.
ethereum/api/src/main/java/org/hyperledger/besu/ethereum/api/query/BlockchainQueries.java