code: func setDefaults(cfg *Config) {
  	if cfg.ChainConfig == nil {
  		cfg.ChainConfig = &params.ChainConfig{
  			ChainID:        big.NewInt(1),
  			HomesteadBlock: new(big.Int),
  			DAOForkBlock:   new(big.Int),
  			DAOForkSupport: false,
  			EIP150Block:    new(big.Int),
  			EIP155Block:    new(big.Int),
  			EIP158Block:    new(big.Int),
  		}
  	}
  
  	if cfg.Difficulty == nil {
  		cfg.Difficulty = new(big.Int)
  	}
  	if cfg.Time == nil {
  		cfg.Time = big.NewInt(time.Now().Unix())
  	}
  	if cfg.GasLimit == 0 {
  		cfg.GasLimit = math.MaxUint64
  	}
  	if cfg.GasPrice == nil {
  		cfg.GasPrice = new(big.Int)
  	}
  	if cfg.Value == nil {
  		cfg.Value = new(big.Int)
  	}
  	if cfg.BlockNumber == nil {
  		cfg.BlockNumber = new(big.Int)
  	}
  	if cfg.GetHashFn == nil {
  		cfg.GetHashFn = func(n uint64) common.Hash {
  			return common.BytesToHash(crypto.Keccak256([]byte(new(big.Int).SetUint64(n).String())))
  		}
  	}
  }
docs: // sets defaults on the config