private File resolveNodePrivateKeyFile(final File nodePrivateKeyFile) {
    return Optional.ofNullable(nodePrivateKeyFile)
        .orElseGet(() -> KeyPairUtil.getDefaultKeyFile(dataDir()));
  }
Returns data directory used by Besu. Visible as it is accessed by other subcommands.

@return Path representing data directory.
app/src/main/java/org/hyperledger/besu/cli/BesuCommand.java