You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: gen_genesis.go
    path of file: ./repos/go-ethereum/core
    
    the code of the file until where you have to start completion: // Code generated by github.com/fjl/gencodec. DO NOT EDIT.

package core

import (
	"encoding/json"
	"errors"
	"math/big"

	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
	"github.com/ethereum/go-ethereum/common/math"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/params"
)

var _ = (*genesisSpecMarshaling)(nil)

// MarshalJSON marshals as JSON.
func (g Genesis) MarshalJSON() ([]byte, error) {
	type Genesis struct {
		Config        *params.ChainConfig                               `json:"config"`
		Nonce         math.HexOrDecimal64                               `json:"nonce"`
		Timestamp     math.HexOrDecimal64                               `json:"timestamp"`
		ExtraData     hexutil.Bytes                                     `json:"extraData"`
		GasLimit      math.HexOrDecimal64                               `json:"gasLimit"   gencodec:"required"`
		Difficulty    *math.HexOrDecimal256                             `json:"difficulty" gencodec:"required"`
		Mixhash       common.Hash                                       `json:"mixHash"`
		Coinbase      common.Address                                    `json:"coinbase"`
		Alloc         map[common.UnprefixedAddress]types.Account `json:"alloc"      gencodec:"required"`
		Number        math.HexOrDecimal64                               `json:"number"`
		GasUsed       math.HexOrDecimal64                               `json:"gasUsed"`
		ParentHash    common.Hash                                       `json:"parentHash"`
		BaseFee       *math.HexOrDecimal256                             `js
    
func (g *Genesis) UnmarshalJSON(input []byte) error {
	type Genesis struct {
		Config        *params.ChainConfig                               `json:"config"`
		Nonce         *math.HexOrDecimal64                              `json:"nonce"`
		Timestamp     *math.HexOrDecimal64                              `json:"timestamp"`
		ExtraData     *hexutil.Bytes                                    `json:"extraData"`
		GasLimit      *math.HexOrDecimal64                              `json:"gasLimit"   gencodec:"required"`
		Difficulty    *math.HexOrDecimal256                             `json:"difficulty" gencodec:"required"`
		Mixhash       *common.Hash                                      `json:"mixHash"`
		Coinbase      *common.Address                                   `json:"coinbase"`
		Alloc         map[common.UnprefixedAddress]types.Account `json:"alloc"      gencodec:"required"`
		Number        *math.HexOrDecimal64                              `json:"number"`
		GasUsed       *math.HexOrDecimal64                              `json:"gasUsed"`
		ParentHash    *common.Hash                                      `json:"parentHash"`
		BaseFee       *math.HexOrDecimal256                             `json:"baseFeePerGas"`
		ExcessBlobGas *math.HexOrDecimal64                              `json:"excessBlobGas"`
		BlobGasUsed   *math.HexOrDecimal64                              `json:"blobGasUsed"`
	}
	var dec Genesis
	if err := json.Unmarshal(input, &dec); err != nil {
		return err
	}
	if dec.Config != nil {
		g.Config = dec.Config
	}
	if dec.Nonce != nil {
		g.Nonce = uint64(*dec.Nonce)
	}
	if dec.Timestamp != nil {
		g.Timestamp = uint64(*dec.Timestamp)
	}
	if dec.ExtraData != nil {
		g.ExtraData = *dec.ExtraData
	}
	if dec.GasLimit == nil {
		return errors.New("missing required field 'gasLimit' for Genesis")
	}
	g.GasLimit = uint64(*dec.GasLimit)
	if dec.Difficulty == nil {
		return errors.New("missing required field 'difficulty' for Genesis")
	}
	g.Difficulty = (*big.Int)(dec.Difficulty)
	if dec.Mixhash != nil {
		g.Mixhash = *dec.Mixhash
	}
	if dec.Coinbase != nil {
		g.Coinbase = *dec.Coinbase
	}
	if dec.Alloc == nil {
		return errors.New("missing required field 'alloc' for Genesis")
	}
	g.Alloc = make(types.GenesisAlloc, len(dec.Alloc))
	for k, v := range dec.Alloc {
		g.Alloc[common.Address(k)] = v
	}
	if dec.Number != nil {
		g.Number = uint64(*dec.Number)
	}
	if dec.GasUsed != nil {
		g.GasUsed = uint64(*dec.GasUsed)
	}
	if dec.ParentHash != nil {
		g.ParentHash = *dec.ParentHash
	}
	if dec.BaseFee != nil {
		g.BaseFee = (*big.Int)(dec.BaseFee)
	}
	if dec.ExcessBlobGas != nil {
		g.ExcessBlobGas = (*uint64)(dec.ExcessBlobGas)
	}
	if dec.BlobGasUsed != nil {
		g.BlobGasUsed = (*uint64)(dec.BlobGasUsed)
	}
	return nil
}