public Optional<Wei> getGenesisBaseFeePerGas() {
    if (getBaseFeePerGas().isPresent()) {
      // always use specified basefee if present
      return getBaseFeePerGas();
    } else if (getConfigOptions().getLondonBlockNumber().orElse(-1L) == 0) {
      // if not specified, and we specify london at block zero use a default fee
      // this is needed for testing.
      return Optional.of(BASEFEE_AT_GENESIS_DEFAULT_VALUE);
    } else {
      // no explicit base fee and no london block zero means no basefee at genesis
      return Optional.empty();
    }
  }
Gets genesis base fee per gas.

@return the genesis base fee per gas
config/src/main/java/org/hyperledger/besu/config/GenesisConfig.java