static ProtocolSpecBuilder.FeeMarketBuilder createFeeMarket(
      final long londonForkBlockNumber,
      final boolean isZeroBaseFee,
      final boolean isFixedBaseFee,
      final Wei minTransactionGasPrice,
      final ProtocolSpecBuilder.FeeMarketBuilder feeMarketBuilder) {
    if (isZeroBaseFee) {
      return blobSchedule -> FeeMarket.zeroBaseFee(londonForkBlockNumber);
    }
    if (isFixedBaseFee) {
      return blobSchedule -> FeeMarket.fixedBaseFee(londonForkBlockNumber, minTransactionGasPrice);
    }
    return feeMarketBuilder;
  }
Provides the various {@link ProtocolSpec}s on mainnet hard forks.
ethereum/core/src/main/java/org/hyperledger/besu/ethereum/mainnet/MainnetProtocolSpecs.java